Accuracy of Stuck-On Thermometers

I presume Olga in Deep Snow and it is STILL COMING DOWN (you can tell that
you are no longer a kid when snow coming down is not celebrated any more :-(
) is referring to the "thermometers" that are "stuck on" the outside glass of
tanks.  If so, they are "calibrated" for a room temperature of about 70
degrees F.  If your room temperature varies quite a bit from evening to
morning, you will get some rather wildly goofy readings!

I tend to trust only the thermometers that are actually in the water.
Additionally I always put the entire batch of new ones in the same tank at
first - that way you can discover the screwy one or more in the batch that
consistently is WRONG.  (Yes, it could be possible that the "screwy one or
more" is RIGHT, and all of the others WRONG!  :-(  
However, I do have a Laboratory Grade Thermometer, purchased at the local
University Chemical Supply Room, that I use to see which of the cheapies is
good, which bad.  :-)  )

Hope this is helpful.