“Speaking of standards, time study is another thing everyone gets wrong.” The typical time study is based on taking 10 times and setting an average time as the standard. Ohno says this is very bad because if you are watching someone do something 10 times and they are doing it differently each time you should stop to correct them right away. This is the kaizen “stop and fix” mentality, extended to time study.
Ohno asks what’s the point of just taking times that are not good times to begin with, when you can take the shortest time as the best time. “Some say that is harsh, but what’s harsh about it?” asks Ohno. “The shortest time is the easiest method.”
The purpose of process observation and time study is not to get an average time and build in the waste and variation to the standard time but to ask why there is variation between different people or between the same person over 10 repetitions of the same process. Ohno is looking at time study not from the standpoint of establishing Industrial Engineering standards but from a kaizen standpoint.
Ohno recommends not including allowances for breaks to go to the toilet. These times are unreliable anyway, he says, so let people go to the toilet when they need so long as they stop the line. The team lead or the supervisor should step in to keep the line going. He says that allowing times to go to the toilet as part of the standard time, whether people need to go or not, just creates slack.
This again is an example of the jidoka (stop the line) principle built into his thinking, influencing how time study should be done. The principles (stop and fix) dictate how the improvement tool (time study) should be used. This is an important lesson.
Ohno ends the chapter by saying that if you have to take several measurements in order to set a standard, use the shortest time. Then find the reasons why this time can not be met and teach them how to make it possible to do it in the shortest time.
Just as the theme from Chapter 6 was “Costs do not exist to be calculated. Costs exist to be reduced” the theme from this chapter could be stated as “Times do not exist to be studied. Times exist to be reduced.”