Had 2 (analog, not digital) since about 2004
Before Katrina (not my daughter - the hurricane), I was very anal about monitoring temps using a graduated cylinder with water in the freezer and a digital thermometer.
I also monitor clarity with a 14-16" cylinder with a sample after I rack to the brite tank - gives me an idea of how the beer is clearing.
Noticed over the last week or so, that even though I had the control set at 36 F (I wanted an average temp of 34 F), that the beer in the cylinder was freezing.
I checked again today, after raising the controller temp to 38, and the beer in the cylinder was freezing again.
I checked with a digital thermometer, and my beer in the cylinder was 30.6 F -- this is where the WTF comes in - 38 on the controller should give me an average temp of 36 F - I just raised it to 40 F and will check again in the morning.
My chest freezer is a GE (they have become a POS) that is only about 2 years old. BUT, the controller should regulate the temps.
I have nothing else in the freezer that would interfere with the probe recognizing what the temp is - it is positioned so that it is in free air space and not touching anything.
Q for the more advanced brewers - should I put the probe in liquid to register the temps better ? (had not done this in the past, and did not have trouble keeping temps within range of what I told the control to do)
Guess the point is, be anal about your temps and use a secondary method to monitor temps. Just setting the control at a certain temp does not guarantee that that is what reality is.
I guess it's like the old expression: "never trust a fart"
Hope this helps some of the newbies and intermediates avoid potential problems (temp showing X, and it's really Y - could interfere with fermentation times)