# What is meant by “accuracy within factor of 2” in sensors?

I've spent quite some time googling the meaning of "factor of (number)" in sensor accuracy but could not find any document explaining the meaning of this expression used to describe sensor accuracy. Specifically, I'm looking for the meaning of "factor of 2" in the below sentence:

"Detectors should respond to gamma radiation photons within any energy range from 60 keV to 3 MeV with a dose rate response accuracy within a factor of 2 over the entire range"

[Extract from NRC Regulatory Guide "Instrument for light water cooled nuclear power plants to assess plant and environs conditions during and following an accident (page 1.97-14)"][1]

I know that accuracy is usually stated like "+/- 2% over the sensor range". This, simple and straight forward expression is easy to understand. For example, if a tachometer has accuracy of +/- 5 rpm over the range of 100 to 1000 rpm and the rpm measured by the tachometer shows 500 rpm, then it can be said that the actual value is within 495 to 505 rpm.

I understand that increase/decrease by a factor of 2 means multiplication/division by 2. Am I correct to say "if the detector indicates 100 keV, the accuracy should be such that the actual value is within 50 keV to 200 keV"?

• That would be my understanding. – Transistor Jun 6 '20 at 14:13
• Thanks for the input! I'm still looking for any documents describing this "factor of (number)" as "+/- (value)(unit)" – Jim Jun 7 '20 at 23:19