We've all encountered a "Duh" moment when we're working with time units.

Many time the problem is that we *forget* that there really aren't 100 seconds in a minute.

That would be the decimal trap.

For example, 4:17 as reflected on a time piece (a.k.a. stopwatch) does not equate to 4.17 minutes. If for some reason, decimals are preferred, like on the “bottom rung” of a value stream map’s lead time ladder, then 4:17 should be reflected as 4.3 minutes. Calculated as follows:

Another common error occurs when clock times are added or subtracted. This is again rooted in decimal confusion. For example, after recording cumulative times on a time observation form, the practitioner must then determine the discrete time for each observed step. This requires subtraction. The difference between 5:02 and 4:17 is not 0.85, rather it is 45 seconds.

I know that these errors seem pretty silly. But, I know that I've made them myself and I have seen folks that are newly introduced to direct observation and the use of time pieces make them - over and over again.