Temp diff between Honeywell thermostat & IR thermometer - uk.d-i-y

Message from discussion Temp diff between Honeywell thermostat & IR thermometer
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From: michaeld...@hotmail.com
Newsgroups: uk.d-i-y
Subject: Temp diff between Honeywell thermostat & IR thermometer
Date: 16 Nov 2006 01:58:16 -0800
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I had a Honeywell CM67 thermostat which gave a temperature reading
about 3 deg C lower than when measured with my IR Thermometer (ie by
pointing it at the thermostat case and display as well as the wall
around it).

I've just replaced the thermostat because of a (different) fault with a
new Honeywell CM907 (the new version of the CM67) and I'm getting the
same thing.  I know that I can change the calibration / temperature
offset, but I wondering why it's happening at all.  Is it something to
do with the way I'm using the IR thermometer?  

Thanks,

Michael