Performetric uses the seven-point USAFSAM Mental Fatigue Scale, created in 1979 by Dr. William F. Storm and Captain (Dr.) Layne P. Perelli of the Crew Performance Branch of the USAF School of Aerospace Medicine, Brooks AFB, San Antonio, Texas, and then used in many field and laboratory tests. The scale items are:
- Fully alert. Wide awake. Extremely peppy.
- Very lively. Responsive, but not at peak.
- Okay. Somewhat fresh.
- A little tired. Less than fresh.
- Moderately tired. Let down.
- Extremely tired. Very difficult to concentrate.
- Completely exhausted. Unable to function effectively. Ready to drop.
Levels 1-3 mean that the individual is not tired, while levels 4-5 indicate the the individual is experiencing some fatigue and levels 6-7 that the individual is really tired which could lead to an unsafe or health-damaging scenario.