9 6 
EMPLOYMENT PSYCHOLOGY 
dividing, and pointing off decimals on a machine is an 
entirely different process from the process involved in the 
mental solution of identical arithmetical problems. In 
fact, a girl who knows nothing whatsoever of division can 
be taught how to divide on a machine in a comparatively 
short time. However, in spite of this fact, it is highly nec 
essary that a comptometrist have a fundamental knowl 
edge of arithmetic. A comptometrist who does not have 
this is far more likely to make errors and to overlook 
errors than one who does. The experiments conducted 
proved this conclusively. An operator who knows arith 
metic can frequently tell when her answer is wrong or 
absurd by a mere inspection. To be specific, the decimal 
point in a calculation done on a machine can be taken 
care of automatically by setting an index or pointer and 
then following certain definite rules as to which rows of 
keys to use. As long as these rules are followed, no mis 
takes will occur. However, when, by chance, the operator 
fails to follow these rules she may obtain a result as fol 
lows: 1468 x .00034 equals 4.9912. Now, the numerical 
answer here is correct, but the decimal point is in the 
wrong place, and unless the operator knows the arith 
metical rules regarding the use of decimals in addition to 
the rules governing the mechanical operation, she may 
see nothing wrong in the above answer. Frequent mis 
takes of this kind were found in the course of the experi 
ments on comptometrists. Such mistakes made in actual 
work are likely to be very costly. Even though mistakes 
in the long run tend to equalize themselves, the fact that 
most of them are not allowed to run long, but must sooner 
or later be corrected, usually with an amount of labor far 
more costly than the errors themselves, makes it very im 
portant to reduce such errors to a minimum. The modern