If you are reading this, you are probably and Industrial engineer, operations manager or consultant who is looking to measure the work performed by their associates for various odd reasons. This article is aimed to serve as guide to help you choose the best work measurement technic for your need and to highlight differences between both.
There are basically two work measurement technics namely Predetermined motion time system (PMTS) and time studies. Let’s start with the definition of both.
PMTS is a database of basic motion elements and their associated normal time values, together with a set of procedures for applying the data to analyse manual tasks and establish standard times for the tasks. The database was created studying thousands of associates of performing various activities and average time for each activity was registered in tabular form. The popular PMTS are, Methods time measurement (MTM), Work factor, Predetermined time standards systems-Meyers, Maynard operations sequence technic (MOST).
Time study is a structured process of directly observing and measuring human work using a timing device to establish the time required for completion of the work by a qualified worker when working at a defined level of performance. Time studies were originally performed using stop watches and eventually with time they are performed by video shooting the activity and studying them.
For this article we will compare MOST (PMTS) and video-based time studies to find out the difference between PMTS and time studies. The points we will cover to find the difference are, Accuracy, Pace rating, Activity types, Allowances and other differences.
Accuracy
When PMTS database was made it was built with maintaining accuracy level that, 95% of the time standard is accurate within +/-5% of the measured time. The problem with accuracy in PMTS is though it is derived by observing thousands of different associates, it needs some balancing time that is needed for the system’s desired level of accuracy to be attained. Now coming to accuracy level in time studies the desired accuracy level can be defined prior to study is conducted. Theoretically there should be no balancing time required in time study as the rates are being found studying demography who will be working there. Higher desired accuracy level in time study will require a greater number of samples which can make the study cumbersome.
Pace rating
“No other component of the time study procedure is subject to as much controversy and criticism as the performance rating phase.”
Ben Niebel
Penn State, 1958
You cannot time-study or set a standard using an exceptional individual. You must use an average person. The rules of doing this properly were never really formalized. In this part I feel that PMTS has an upper hand on time studies. The PMTS database are built by studying thousands of associates, so it is safe to assume various methods of doing same task is captured there and time we get is for average person capable of doing the work. In time studies we must observe the method of each associate doing work and determine who is safely doing it fastest, slowest and at average rate. We then must adjust the found rates to the average working individual capable doing the task whole work day.
Type of work and activities
Though PMTS has considered all the basic, general, controlled, tool and equipment use motions while building the database, there will be certain situation where you will be unable to find the right time for doing any activity. In this case you will have to either, determine the time using similar activity in the database, or use combination of different activities in database or sometime even you may have to build database for your activities on your own following the guidelines. In time studies you will never face this situation as you will be directly observing the activity and determining the time required for it.
Allowances
A standard is just a normal time if allowances for personal, fatigue and delays (PFD) are not added to them. The rates found using PMTS does not have any allowances included in them and it is just and normal time. In both PMTS and time studies after determining the normal time we must add personal and fatigue allowances using Russell Currie’s book, “Work Study”. There may be some other methods to determine the personal and fatigue allowances but Russell Currie’s book, “Work Study” is gold standard in defining allowances. Apart from this the other avoidable and non-avoidable delay are to be observed and need to be factored in PMTS, but in time studies they can be directly included as a part of normal time or removed as required.
There is an extra effort in PMTS to observe and define the other avoidable and non-avoidable delays and factor them in the standard.
Other differences
The other interesting difference between the PMTS and time study is the visibility of the non-value adding activities in any process. PMTS has less visibility to the NVAs as it largely depends on the balancing effect which is the leveling of individual deviations for a smaller overall deviation over time, through which after certain time overall normal time for any activity falls around certain average value. Here, there is possibility that the engineer doing analysis using PMTS may consider the large variation occurring in any activity as smaller deviation and leave it in the hands of balancing effect. This large variation which is considered as small variation are actual NVA which if reduced can improve the cycle time. In time studies especially in video-based time studies it is difficult to neglect the large variations and you can easily differentiate between these small and large variations to take steps to reduce these NVAs. Even finding best practice to do any work is easy in video based time study and not in PMTS.
