experiments with motormen, no one has gone through those 12 cards in a
shorter time than 140 seconds, while the longest time was 427 seconds.
On the other hand, no one of the motormen made less than 4 omissions,
while the worst ones made 28 omissions. I abstract from one extreme
case with 36 omissions. On the whole, we may say that the time
fluctuates between 180 and 420, the mistakes between 4 and 28. The aim
is to find a formula which gives full value to both factors and makes
the material directly comparable in the form of one numerical value
instead of the two. If we were simply to add the number of seconds and
the number of omissions, the omissions would count far too little,
inasmuch as 10 additional omissions would then mean no more than 10
additional seconds. On the other hand, if we were to multiply the two
figures the omissions would mean by far too much, as the transition
from 4 mistakes to 8 mistakes would then be as great a change as the
transition from 200 to 400 seconds, that is, from the one extreme of
time to the other. Evidently we balance both factors if we multiply
the number of omissions by 10 and add them to the number of seconds.
The variations between 4 and 28 omissions are 24 steps, which
multiplied by 10 correspond to the 240 steps which lie between 180 and
420 seconds. On that basis any additional 50 seconds would be equal to
5 additional omissions. If of two men one takes 100 seconds less than
his neighbor, he is equal to him in his ability to satisfy the demands
of the service, if he makes 10 mistakes more.

On the basis of this calculation I find that the old, well-trained
motormen come to a result of about 450, and I should consider that an
average standard. This would mean that a man who uses 400 seconds
would not be allowed to make more than 5 omissions, in 350 seconds not
more than 10, in 300 not more than 15, in 250 not more than 20, under
the condition that these are the results of the first set of