Warm-up Regulator Resistance Measurement

[msumbry@spacecom.af.mil (HQ AFSPC/IG)]

Vehicle: '79 5KS, 2.2L, Fuel Injected
Background: Haynes manual states resistance measurement for warm-up 
regulator should be 20K ohms. The reading supposedly indicates the 
functional condition of the regulator.
Fact: Measured resistance is 18k ohms on one regulator; 19k on another.
Environment: Ambient temperature around 30-32 degrees F.; meter was
calibrated correctly for zero ohms.
Question: Is there some tolerance for the resistance measurement?
e.g. Plus/minus ?? ohms.
Or, perhaps a better question - should the measurement simply exceed 20k?