Difference between Value and Objective

The difference between ‘value’ and ‘objective’ could be described as below:


• Characteristic of culture
• Finds emotional attachment
• Understood more at sub-conscious level
• Implied intangibly and manifests in human behavior
• Followed inwardly


• Characteristic of result
• Finds intellectual attachment
• Understood more at conscious level
• Implied tangibly and manifests in plans
• Followed outwardly

Maintenance Management Quiz

Evaluate your basic understanding of the maintenance management functions through the following quiz?

To answer, please fill in, tick or explain as per the requirement.

(1) An important statement, such as “achieving maximum plant availability at minimum cost” can be regarded as ………………………………….

(2) The ratio of ‘MTBF’ to ‘MTBF + MTTR + MWT’ is supposed to be representing ………………………………………….

(3) The stages during which 80% of the whole life cycle costs of an asset get decided are described as …………………………………………

(4) A popular methodology of ‘Root Cause Analysis’, used to establish causes for maintenance problems, is based on diagrams and frequently called as .…………………

(5) If the failure of a system is given as the sum of the individual failure rates of different elements constituting the system, then the configuration of the system is called as

(6) A fixed time replacement policy is usually suggested for an item with random failure characteristic showing a constant probability of failure at all ages. True or False?

(7) Do we need to improve maintenance productivity in industry? Why?

(8) What will happen if MTBF of a machine in your department gets reduced?

(9) The sum of direct maintenance cost and indirect maintenance cost is called as

(10) The ‘Up Time’ of a machine on four consecutive occasions was noticed as UT1, UT2, UT3 & UT4.

If X = (UT1 + UT2 + UT3 + UT4) / 4
Then, X will represent ………………………..

(11) The ratio of ‘Capital Investment’ to ‘Profit’ is known as …………………………..

(12) When maintenance is done only because it needs to be done since it has already been planned and scheduled, or because that is an established practice though, in real sense, there may not be any need of it, then such type of maintenance can be referred as ………………………………………..

(13) In maintenance stores, the inventory of ‘C’ class of items in terms of money value is often found lower than that of ‘A’ or ‘B’ class items in different companies. True or False?

(14) The art of directing and inspiring people and the process of getting things done through them is usually referred as ……………………………………

(15) The purpose of planned maintenance is mainly to reduce breakdowns and downtime but not necessarily the total maintenance cost. True or False?

(16) Conventionally, in many plants, maintenance activities are devoted to achieving maximum plant availability which is influenced by the down time losses only. However, there are other equipment losses also which are frequently found present in many cases. It’s therefore equipment availability alone cannot formulate the correct parameter for evaluating the overall equipment performance. True or False?

(17) Roughly, what (%) may be the ‘Inventory Carrying Cost’ in your company’s stores as per your guesstimate?

(18) Maintenance technique which is usefully employed not only to reduce downtime due to excessive shutdowns but also to reduce downtime due to excessive breakdowns is frequently known as …………………………………………

(19) For many industries operating in a developing country like ours, the ratio of cost of maintenance materials to cost of maintenance labour may be found in the range of about 70% (maintenance materials) to 30% (maintenance labour) or alike. True or False?

(20) An accident occurs when an unsafe condition is combined with an unsafe act. Many safety surveys indicate that eighty to ninety percent of the accidents are caused due to “unsafe conditions”. Therefore, “unsafe conditions” constitute the major cause for most of the industrial accidents. True or False?

(21) Certain maintenance activities that turn out to be uneconomical in a developed country can very well become economical in a developing country. Why?

(22) What is the characteristic of equipment design that is generally represented by MTBF?

(23) Preventive maintenance carried out on scheduled fixed-time basis is often likely to have elements of both over maintenance as well as under maintenance. In order to control ill effects of both over maintenance and under maintenance, the concept of condition-based Predictive Maintenance was evolved and recommended by the experts. True or False?

(24) Statements, such as, “I am working in the maintenance department for the last 20 years. I know my problems best. Nobody else can do the way I have been doing. What more can you expect from me!” are supposed to represent ………………………………..

(25) Once the daily maintenance work is recorded in a log book, there is practically no need to transfer it to the respective history cards, and if somebody is doing so, he is fruitlessly duplicating the work. True or False? Why?

(26) The ratio of ‘Output’ (representing production) to ‘Input’ (representing ‘3M’ resources) is popularly known as …………………………………….

(27) Knowing in advance “What” and “Where” is going wrong in different machines does not help much because if any breakdown is to occur, it will occur certainly. True or False?

(28) A machine, for which both MTTR and MTBF are high, is likely to yield low
machine availability. True or False? Why?

(29) The technique that is based on infrared radiation to detect hot spots or high
temperature conditions in various plant equipment is called as ………………..

(30) Readings about vibration amplitude were taken on an equipment at different time
intervals. A higher vibration will directly reveal the cause of trouble through such
readings. True or False?

(31) The ‘Down Time’ of a machine on four consecutive occasions was noticed as DT1, DT2, DT3 & DT4.

If Y = (DT1 + DT2 + DT3 + DT4) / 4
Then, Y will represent ………………………………

(32) For effective lubrication programme, the following “5 Right” things are always considered essential:

(i) Right Type
(ii) Right Quantity
(iii) Right Method
(iv) Right …………
(v) Right …………

(33) Good maintenance can often result in lower consumption of electrical power. For example, worn out pumps or motors running on loose V-belts, etc. are supposed to consume more electrical power. True or False?

(34) A Gantt Chart forever provides better effectiveness in planning & scheduling various activities of a maintenance job compared to PERT/CPM.

(35) The inventory carrying cost in the stores of a company was estimated at 20%. However, the yearly inflation rate was recorded close to 7%. If an item is kept in the stores for a period of 1 year, how much more will it actually cost compared to its original price after 1 year?

(36) The third generation findings prove that failure rate of an item (or in other words, reliability of the item) does not always depend on its operating age. True or False?

(37) Bathtub curve describes a particular form of the hazard function and indicates failure rate pattern observed in some products during their lifetime which comprises of three distinctive parts. True or False?

(38) If stock-in cost for an item is more than its stock-out cost, then there is no need to stock the item in stores. True or False? Why?

(39) RCM technique advocates if the criticality of a failure falls in insignificant category, it can be left to “run to failure” strategy. True or False?

(40) If availability of a machine is influenced by its reliability, what is the other machine characteristic that also affects its availability?

(41) Which one of the following statements explains the meaning of ‘Preventive Maintenance’ in a better way:

(i) Replacing failed parts with new parts when required.
(ii) Finding defects of the machine before breakdowns.
(iii) To anticipate machine defects & failures in advance and take
proper proactive action before they get converted into breakdowns.

(42) During 20th Century, improvement in productivity was considered much necessary. However, during 21st Century, improvement in productivity has proved more or less meaningless because profitability is supposed to be of greater value. True or False?

(43) The approach which is a combination of management, financial, engineering and other practices applied to physical assets in pursuit of economic life-cycle costs; that is concerned with the specification and design for reliability and maintainability of plant, machinery, equipment, buildings and structures, with their installation, commissioning, maintenance, modification and replacement, and with feedback of information on design, performance and costs is known as …………………………………………

(44) The more the maintenance workload in a maintenance department, the better will be the management of maintenance function. True or False? Why?

(45) At high pressures with impact conditions, the abrasion that involves removal of sizeable particles from a surface by the action of a coarse abrasive material is called as

(46) The time interval between the point at which the onset of failure can be detected and the point at which functional failure occurs is called as……………………..

(47) A failure mode describes how equipment can fail and potentially result in a functional failure. True or False?

(48) The science and practice of wear, friction and lubrication applied to engineering surfaces in relative motion is called as …………………………………..

(49) Third generation research originally carried out by two Americans, Stanley Nowlan and Howard Heap revealed that not one or two but “Six Failure Patterns” actually occur in practice. True or False?

(50) The maintenance practice which suggests that maintenance should ideally be carried out just at that point of time when plant equipment and machinery actually requires maintenance is called as ………………………………………

(51) The wear mechanism that is attributed to the cyclic loading of two surfaces in mutual contact and usually occurs without prior indication of major loss of the surface material is known as ……………………………………………

(52) A failure mode whose failure effects do not become apparent to the operators
on its own under normal circumstances is known as ………………………………………

(53) In a system involving a pump, coupling and a motor, the reliability of each component is 90%. In such a case, the reliability of the overall system (pump-coupling-motor together) will be much less than 90%. True or False?

(54) In complex systems, as high as 60% cases represent “Bathtub” type of failure pattern. (Tick):

(55) The probability of failure – free operation of a machine within a given time and specified working conditions is called as……………………………………

(56) A process that is used to determine “What maintenance must be done” to ensure that a physical asset continues to fulfill its intended functions in its present operating context,
is called as……………………………………………..

(57) Why should V-belts be avoided to run in loose condition? How Flat belts become preferable over V-belts in certain cases?

(58) In brainstorming, the role of logic should start after the creative process gets over. We should use our logic in separating out the useful ideas from the list of brainstormed ideas and finally in evaluating them for proper selection. True or False?

(59) In order to effect reduction in overall inventory of maintenance stores, we need to be guided by the broad principles, viz. (i) “Reduce Consumption Cost” of maintenance items (ii) “Reduce Stocking Cost” of maintenance items. True or False? Why?

(60) TPM is somewhat analogical to family team approach where all family members are ready to co-operate and act as a harmonious team to contribute to common objectives and solve problems jointly. For example, in TPM, both production and maintenance need to share a common objective, i.e. maximum overall equipment effectiveness. True or False?

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Insight into Overall Equipment Effectiveness (OEE)

Basically, Overall Equipment Effectiveness (OEE) indicates overall performance of an equipment and calculated by multiplying factors, viz. “Availability Performance”, “Speed Performance” and “Quality Performance”.  OEE is frequently shown by the following formula:

OEE = Equipment Availability x Performance Efficiency x Rate of Quality Products

Or, OEE = A x P x Q

Broadly, OEE of a machine indicates “Potential” utilized vis-à-vis its “Total Potential”. For example, if OEE of a machine is 70%, it clearly indicates that 70% of the “Total Potential” of the machine is only being utilized presently and the rest 30% is simply wasted in various forms, commonly known as machine losses, i.e. six big losses. In other words, we could also say that 30% of the “Total Potential” of the machine remains untapped or unutilized.

We could go a step further. Suppose, there is a machine having capital investment of 2 crores of rupees and showing 50% OEE only, then it will mean that this machine though has potential to produce “X” quantity, yet it’s only producing “0.5 X” acceptable quantity. In other words, whereas half of the capital investment of 1 crore of rupees is producing return, the rest half of the investment is not at all generating anything.

In other words, OEE represents “Net Utilization” of a machine in the form of ‘o.k.’ production, and not as total production which equals ‘o.k.’ plus ‘reject’ production.

Of late, some specialists suggested to modify the OEE formula as follows:

OEE = Equipment Availability x Performance Efficiency x Rate of Quality Products x Energy Consumption

Or, OEE = A x P x Q x E

In order to critically analyze the usefulness of the above formula, we need to get answers to few questions. Firstly, we need to ask a very basic question – “What is the purpose of including ‘E’ in OEE?” 

“Is it to improve ‘E’ or ‘OEE’ or ‘Both’?” 

If your answer is to bring about improvement in ‘Both’, will you then say that only by including ‘E’ in OEE formula, both of them can be improved effectively?

“What is your answer?” 

According to us, the reason why ‘E’ is being suggested for including in OEE formula is to improve ‘E’ only and not ‘OEE’. And that is why we do not favour to include ‘E’ in OEE formula. Further, any variations in A, P & Q in the traditional OEE formula directly affect ‘Volume of Production’. However, any variation in ‘E’ does not directly correlate to variation in ‘Volume of Production’. As such, when ‘E’ is influenced by OEE and OEE is not influenced by ‘E’, then including ‘E’ in OEE formula seems illogical.

It’s therefore ‘E’ factor does not find any compatibility with A, P & Q factors. Further, if ‘E’ factor is included in OEE formula, it will also become difficult to pinpoint the specific reasons for poor OEE performance.

Therefore, let us keep improving OEE in the traditional way by enhancing A, P & Q. And, also let us keep improving ‘E’ separately without including it in OEE formula, the way most industries have already been doing it traditionally. Let the reigns of controlling or improving ‘E’ (Energy Performance) exclusively remain in the expert hands of Energy Manager or Manager (Electrical) or someone else better considered by the management of the company.

To tell you further, some other specialists speculated it slightly differently that OEE with energy can be termed as OEP. They suggested that the energy intensive units can measure the performance in terms of OEP in stead of OEE as indicated below: 

OEP = A x P x Q x E

Where, A x P x Q = OEE

Or, OEP = OEE x E 

By looking at the above formula, again it’s difficult to get convinced and therefore we need to find answers to some of the questions once more as noted below: 

 (A) Would you like to recommend only OEP for energy intensive units? Or

(B) Would you prefer to recommend both OEE and OEP for energy intensive units?

In case, you select (A) – “Could you please apprise us what & how will you be going to analyze OEP data to arrive at useful conclusions to devise further action for equipment improvement?”

However, if you fall for (B), our next question is – “Will it be better to have OEE & OEP data, or just OEE & ‘E’ data separately?” Please explain with your reasoning.

After finding answers to the above stated questions, we believe that you will also like to go in for OEE & ‘E’ data separately for improving both of them effectively. We don’t see any necessity of including ‘E’ in OEE formula irrespective of whether it’s energy intensive industry or not.

It seems futile when specialists suggest to change OEE formula by including ‘E’ factor. In the detailed analysis given above, things have been presented logically and it can be concluded that there is no need to include ‘E’ in OEE formula because it will not only change the basic concept and content of OEE but also make things unnecessarily complicated without any real benefits.

However, if you wish to integrate OEE and ‘E’ in a fruitful manner, we would like to suggest a KPI, i.e. [Ratio of ‘E (Energy Consumed)’ to ‘OEE (%)’] for monitoring performance of ‘E (Energy Consumed)’ for a machine in a periodic manner. Such a KPI will actually show performance of ‘E (Energy Consumed)’ in achieving ‘1% OEE’ of a machine. Obviously, a decreasing trend of this KPI will represent better performance of ‘E (Energy Consumed)’.

What is TPM?

Total Productive Maintenance, as a means of introducing a new maintenance regime, is centred on optimum mix of different techniques, approaches and ideologies that lay emphasis on organizing improved and efficient form of productive maintenance through total participation of plant people.

TPM perception is unequivocally farsighted, which advocates that a facility cannot be kept in good working condition through certain fixed procedures, but by way of autonomous action only. It focuses on overall equipment effectiveness in terms of availability, output and quality performance factors. TPM also recommends to disciplining unity in the efforts of key departments, such as operation, maintenance, planning, design, etc. to discover the best results of economy in the usage of plant equipment and facilities throughout their life cycle.

TPM aims at arresting all kinds of equipment losses and wastage as it stands for zero defects, zero breakdowns and zero losses. It’s focused on maximizing “Overall Equipment Effectiveness (OEE)” of various machines. In essence, TPM represents total productivity improvement of various resources to enable maximizing return on investment.

Often, the benefits of TPM are phenomenal. It means working for improved knowledge, skills & culture to be able to realize higher output together with better quality from the existing machine resources at lesser cost. It adds to the overall economics in a big way and sharpens competitiveness of the company.

Based on the past experience, generally 10 to 25% production capacity of different machines is lost in various ways which is often found beyond the normal understanding of many plant people. Evidently, therefore, if such hidden or unnoticed losses are identified and controlled, additional plant capacity for higher production can simply be created from the existing resources of plant equipment and machinery. And, that is one of the prime objectives in following TPM approach and improving machine performance by collecting and analyzing OEE data. The impact of merely 1% loss of capacity in many plants is simply enormous.

 As such TPM requires involvement of all plant people from top to the bottom. It stands for improving plant together with plant people and creating a pleasant work environment. In other words, it requires both technical and cultural changes. It relies on autonomous small group activities.

The success of TPM is dependent on how cohesively everybody can be an integral part of the TPM programme. It always requires concerted effort to firmly establish TPM culture in a plant. It requires development of plant people with right attitudes, willingness, enthusiasm and ownership, well equipped with adequate knowledge & skills, together with unmatched team spirit to be successful in achieving the desired results. It often takes quite some time before TPM gets firmly rooted and all plant people really become part of the TPM programme.

What is RCM?

Reliability-centered Maintenance (RCM) is a process to ensure that assets continue to do what their users require in their present operating context. Reliability-centred Maintenance is one technique more within the possibilities to develop a maintenance plan in an industrial plant that it has some advantage over other techniques. Initially, it was developed for the aviation sector in USA, where the high costs involved in the systematic replacement of parts threatened the airlines profitability. Later, this technique was transferred to the industrial field after establishing some excellent results in the aeronautical field.

The reliability-centred maintenance is based on failure analysis, both those that have already happened and being tried to avoid with certain preventive actions, and finally those that have a certain probability of happening and that can have serious consequences. RCM can be used to create a cost-effective maintenance strategy to address dominant causes of equipment failure. It is a systematic approach to defining a “Routine Maintenance Programme” composed of cost-effective tasks that are planned and scheduled to preserve important functions of various plant equipments. The important “functions” of various equipments to preserve with routine maintenance are identified, their dominant “failure modes” and “causes” determined and the “consequences” of failures ascertained. Levels of “criticality” are assigned to the consequences of failure. Some functions are not critical and are left to “run to failure” while other functions must be preserved at all cost. Maintenance “tasks” are selected that address the dominant failure “causes”.

The RCM method employs Planned Preventive Maintenance (PPM), Predictive Maintenance (PdM), Breakdown Maintenance (also called reactive maintenance) and Proactive Maintenance techniques in an integrated manner to increase the probability that an equipment will function in the required manner over its design life-cycle. The goal of the method is to provide the required reliability and availability at the lowest cost. RCM requires that maintenance decisions be based on maintenance requirements supported by sound technical and economic justification.

RCM analysis determines the “type of maintenance” appropriate for a given item of an equipment. It results in a decision of whether a particular piece of equipment should be reactively maintained (“Accept the Risk of Failure” and “Repair after Failure”), preventively maintained (“Prevent the Failure” by “Defining PM Task and Schedule”) or predictively maintained (“Predict & Correct the Failure” by “Defining PdM Task and Schedule”) or proactively maintained.

Successful implementation of RCM leads to improvement in cost effectiveness, machine uptime, and a greater understanding of the level of risk that the organization is managing.

Failure of Coal Crusher Bearings : Case Study

This case is related to a coal crusher with crushing capacity of 50-60 tonnes per hour. The prime mover of the crusher incorporated a 50 H. P. motor and operated at 500 R.P.M.

The crusher was operated through belts and pulleys on both sides and supported by four no. of double row spherical roller bearings A, B, C & D housed in pillow blocks as shown in the sketch below.

A fly wheel on each side of the crusher was also installed at the extreme ends to provide higher moment of inertia as shown in the sketch.


The observations showed that the bearings used to fail once in one or two months after running hot. The bearings B & C were found more prone to failure than A & D bearings.

The leakage of the coal dust from the casing of the crusher along shaft was also observed. Multipurpose grease was used for lubrication of the bearings. The grease container was often found uncovered in close vicinity of the crusher.

Therefore, the reasons for premature failure of the bearings were investigated and appropriate corrective actions to improve life of the bearings were suggested.

Coal dust which is highly abrasive in nature was found leaking from the casing along shaft and found entry into the bearing housings. The bearings B & C were found prone to higher failure due to easy access to leaking dust compared to A & D bearings. The problem was further aggravated due to grease container frequently found lying uncovered near the crusher and thus resulted in the contamination of the grease with coal dust. Undoubtedly, using such contaminated grease led to high abrasive wear of the bearings.

The following corrective measures were suggested to reduce the frequency of bearing failures:

(1)   The leakage of coal dust from the casing of the crusher needed control by providing adequate sealing arrangement.

(2)   The sealing arrangement of the bearing housings needed regular check for effective maintenance.

(3)   Grease container required storing far away from the coal crusher and the dusty environment. It also required to be kept properly covered to avoid any contamination.

The above stated suggestions helped to reduce bearing failures substantially. Subsequently, it was also recommended to control excessive vibrations, poor mounting practices, etc., if any, to ensure increasingly better results.

Failure of Shaft and Bushes : Case Study

A machine incorporated a shaft made of high carbon high chromium hardened steel housed in a cast iron casing. The shaft operated with a reciprocating sliding motion over two phosphor bronze bushes.

The machine faced problem of excessive wear of the bushes together with the shaft. Consequently, the bushes required replacement as early as three weeks whereas the shaft needed replacement quarterly. The machine operated in a dusty environment.

What could be suggested to increase the life of the bushes and the shaft?

As a solution, various alternatives could be evolved to increase the lifespan of the bushes and the shaft. The wear of the bushes could be reduced considerably if bushes made of steel or stellite or linear ball bushes are used in place of phosphor bronze bushes. The linear ball bushes have hardened chrome plated steel balls arranged in helical form and provide easy rotary and axial movements. Thus, one of the best alternatives could be found in using linear ball bushes since they involve little wear & friction and have capacity to take more wear than a conventional bush. Also these bushes provide more effective lubrication due to the spacing between the shaft and the bush. The abrasive dust will also not prove much harmful as it will get trapped in the ball cage of the bush.

The wear of the shaft can be reduced by hard chrome plating. The hard chrome surface improves hardness and ensures reduced friction. The shaft also needs to be provided with seals to check any dust ingression.

Approach for Reducing Plant Failures and Downtime

The following important suggestions comprising a broad approach were given to a particular plant with a view to reduce failures and downtime:

  • Work out ‘Pareto Analysis’ of downtime and production loss to establish priority.
  • Recording of failures along with fault finding and rectification time. Highlighting difficulties encountered while correcting faults.
  • Analyzing records and work out alternative ways to reduce MTTR of various failures.
  • Preparation of ‘Trouble Shooting Charts’ for critical equipment based on the past experience to facilitate maintenance gang to avoid excessive time in fault finding.
  • Introduction of proper training programmes for maintenance workforce with a view to achieve minimum repair time and error free maintenance.
  • Introduction of effective spare parts management with a view to avoid delay due to want of spare parts & tools.
  • Simplification of maintenance procedures so that maintenance gang can straightway start repair work without any waiting or delay.
  • Investigation of failure causes and downtime for each type of failure and comparison to the previous history.
  • Introduction of effective preventive & predictive maintenance activities, such as lubrication, inspection, condition monitoring and tests.
  • Procurement of all necessary special tools and instruments as per the requirement of various maintenance jobs.
  • Issuing proper operating instructions to the operators and maintenance instructions to the maintenance gang.
  • Introduction of maintenance material & spare parts procurement plans, inspection procedures and proper storage together with efficient methods for issuing spare parts & tools to the maintenance gang.

World Class Ratio of ‘Maintenance Labour’ to ‘Maintenance Material’ cost in industry

Basically, the ratio of ‘Maintenance Labour Cost’ to ‘Maintenance Material Cost’ is found varying from job to job, plant to plant and country to country. Further, this ratio will often be seen varying significantly from developed to developing countries.

The nation wide average ratio of ‘Maintenance Labour Cost’ to ‘Maintenance Material Cost’ in a DEVELOPED COUNTRY may be found around 60% : 40% or 65% : 35%, or alike. Whereas the nation wide average ratio of ‘Maintenance Labour Cost’ to ‘Maintenance Material Cost’ in a DEVELOPING COUNTRY will usually  be found in the reverse order, i.e. 35% : 65% or 40% : 60% or alike.

Because of different economic conditions, distinctively different cost patterns are shown in developing and developed countries. However, an important conclusion can be drawn that developed countries, on an average, incur more cost on “Maintenance Labour” as compared to that on “Maintenance Materials”. On contrary, developing countries, on an average, incur less cost on “Maintenance Labour” compared to that on “Maintenance Materials”.

The above facts necessitate developed and developing countries to follow different maintenance strategies to be able to perform economically in their respective environments.

It is therefore there can hardly be any world class ratio due to wide variation across industries as well countries that can truly be acceptable as a world class benchmark for all companies round the globe. Even if such a benchmark is suggested for a developed country, the same cannot exactly be adopted for a developing country or vice versa.

Then, what!

Probably, a better way out could be to measure your own ratio and subsequently strategize to improve it the way you wish to improve it to gain higher economic advantage.

Do simple “averages” of spares serve usefully in Spares Inventory Control?

In spares inventory control if simple “averages” are used to get to know the average consumption of various spares, it may prove quite harmful. Let us take a simple example to explain it further.

Suppose, in a particular case, average consumption of a spare part is found to be 0.5 per month (i.e. 1 part per two months), then if some body uses this “average” metric simply to calculate “annual requirement” of this item as 0.5×12 = 6 parts, it’s likely to be erroneous. In actual practice, the real consumption pattern of this spare part may be found varying widely, e.g. from a “MINIMUM – substantially less than 6 parts (may be even 3 parts or less)” to a “MAXIMUM – substantially more than 6 parts (may be even 12 parts or more)” because statistically consumption of spare parts frequently follows Poisson’s Distribution.

It’s therefore simple “average” consumption of a spare part that follows Poisson’s Distribution cannot be straightaway used to calculate its total consumption/requirement for a future time period, such as a year, or so. Simple “averages” in such cases are likely not to work out trustworthy or friendly.

However, there may be certain regularly used items, such as common maintenance consumables, production raw materials, etc. which may follow Normal Distribution in their consumption patterns. In such cases, simple “averages” may be far more authentic or friendly in calculating total consumption of various items for a future time period, such as a year, or so.