Radio Shack 22-218 Owner's Manual page 20

MAKING ACCURATE MEASUREMENTS
For the most accurate reading, the temperature should be be-
tween 43°F and 74°F (6°C and 23°C) with an 80% maximum
relative humidity.
Keep the meter lying flat on a non-metallic surface. Also, use
a range setting that results in a reading in the upper third of the
meter scale.
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