Originally Posted by jeffeb
If your liquid-in-glass (LIG) thermometer is not calibrated or certified (to NIST or ASTM), then you cannot know its accuracy. Because you do not know its accuracy, how do you know which one is reading correctly? Hypothetically, if your thermometers were only accurate to +/-1 deg C, then a difference of 2 deg C would still be within specification, because (24+1)=(26-1).
Your scale divisions will most likely be every 0.5 degrees (or 0.2 or 1.0). This scale solely determines the thermometer's resolution, not its accuracy.
Your thermometer will also be the partial immersion type which is inherently less accurate than a full immersion type.
Other folks have suggested purchasing the RH Designs digital thermometer http://www.rhdesigns.co.uk/darkroom/...ermometer.html. I can't see what the advantage of this is, because its quoted accuracy is still only
+/-1 degC over the temp. range of darkroom chemicals.