The work measurement methods chosen for each individual situation to be measured depends on several factors which include:
The length on the job to be measured in time units
The precision which is appropriate for the type of work in terms of time units (i.e. should it be in minutes, hundredths or thousandths of a minute)
The general cycle-time of the work i.e. does it take seconds, minutes or days to complete
The length of time necessary for the completion of the range of jobs can vary from a few seconds in highly repetitive factory work to several weeks or months for large projects such as major shutdown maintenance work on an oil refinery. It is quite clear that using a stop-watch, for example, on the latter work would take several man-years to time to measure! Thus, more “overall” large-scale methods of timing must be employed.
The precision is an important factor, too. This can vary from setting times of the order of “to the nearest thousandth of a minute” (e.g. short cycle factory work) to the other end of the scale of “to the nearest week” (e.g. for large project work).
These are the dominant factors that affect the choice of method of measurement.
The Work Measurement Methods
PMTS: At the “precision” end of the scale is a group of methods known as predetermined motion time systems that use measurement units in ten-thousandths (0.0001) of a minute or hundred-thousandths of an hour (0.00001 hours).
The resulting standard times can be used directly, for very short-cycle work of around one minute total duration such as small assembly work. However, they often are used to generate regularly used basic tasks such using assembling or disassembling nuts and bolts, using a screwdriver and similar. Tasks of this type are filed as standard or synthetic data-banks. Estimating:At the other end of the scale (long-cycle and project work) we need something which is quick to use. Such a method is estimating. This can exist in three main forms.
Analytical estimating relies on the experience and judgment of the estimator. It is just of case of weighing up the work content and, using this experience, stating a probable time for completion, such as “this job will take about eight days to complete”. Category estimating: This is a form of range estimating and requires a knowledge of the work. Estimators may not feel comfortable with overall, analytical estimates upon which may depend the outlay of a great deal of money. They often prefer giving a range estimate such as “this job should take between 12 weeks and 14 weeks to complete”, which provides a safety net should things go wrong. Such ranges are not just picked upon at random but are statistically calculated and based on probability theory. Comparative estimating: This is another example of range estimating. Again, estimators rely on the experience of the work in order to produce estimates. This experience can be augmented by the provision of each time-range with a few typical, descriptive, jobs that would guide estimators to the most appropriate range. The estimator would compare the work to be estimated with those in the various ranges until the most appropriate fit is found.
The intermediate method between the two groups above is timing the work in some way, usually with a stop-watch or computerised electronic study board. This method is retrospective in that the job must be seen in action in order to be timed whereas the other methods are prospective and can be used for timing jobs before they start.
The observer times each element of the work and obtains times that the observed operator takes to do the elements. Each timing is adjusted (rated) by the pace at which the operator was working as assessed by the observer. This produces basic times for the elements and hence the whole job, which are independent of the operator and can be used as the time for a trained, experienced worker to carry out the same elements.
Another method of assessing the work is using activity sampling and rated activity sampling. This is a method based on the observer making snap observations at random or systematic sample times, observing what the operator is (or operators are) doing at the times of those observations.
A most useful method for standard or synthetic data-banks of job or element times is using computer models of the jobs. These are generated as mathematical formulae in which the observed data are inserted to compile a time for completion of the task or project. It is a useful method for recycling time standards for elements of basic work over and over again, only changing the values of the variables to suit each project.