EMPLOYMENT PSYCHOLOGY 
illustrates several principles which it is well to bear in mind 
in devising any performance test (46). 
The instrument consists of a battery of four skeleton guns, with 
training or pointing gear, a mechanism for giving the targets a 
series of harmonic wave motions of great variety and complexity, 
a recording device, that shows each movement of the target and 
the corresponding movements of the gun as the pointer or trainer 
tries to follow it, and a firing device, that not only indicates the 
accuracy of the pointing but also the effect of the effort to fire on 
the pointing coordinations. 
Points to be noted regarding this test are: 
1. The task is closely analogous with the job. 
>. The instrument is self-recording, the performance 
being subject to later inspection and analysis. 
3. The apparatus is useful for training. With it the man 
can train himself and does not require the constant atten- 
dance of an officer or experienced operator during the prac- 
tice periods. It also releases expensive and limited equip- 
ment for active service. 
ORDER OF ITEMS 
When the items of a test are of practically the same diffi- 
culty, their order may be determined by chance, but the in- 
vestigator should assure himself by preliminary trial that 
the items really are approximately equal in difficulty. 
The preliminary order may be based on the judgment of 
the investigator. The relative difficulty of the items may 
then be determined by finding the percentage of a group 
that solves each one correctly, or by finding for each item 
the average time required to do it. 
If some items are harder and others easier, they ought to 
be arranged in order of difficulty. When the easiest items 
are placed at the beginning of a test, the subject quickly 
becomes adapted to the test requirements and a better dis- 
tribution of scores is obtained. A number of hard problems 
at the beginning of the test discourages some persons to 
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