Ha ha, Cynthia knows rooster have balls, we showed them to her during butcher day. They're there, they're just not hanging under the bumper.
Thermometers that are glued into a plastic holder with the numbers on the plastic holder, THOSE cannot be trusted. All you have to do is glue the numbers on in the wrong place and your temps are wrong.
I buy cheap dollar store thermoms, remove the glass tube from its plastic surroundings, then stick the glass tube (usually 2 or 3 at once) in a cup of warm water along with my MEDICAL thermometer. When the MEDICAL thermometer hits 100F, I make a mark, right on the glass tube, with a Sharpie, right where the red liquid has risen to. That mark is 100F. I know one hair above or one hair below I will tolerate. Two hairs above or below, I fiddle with my wafer.
Do this in a Styrofoam or plastic cup, not a ceramic coffee cup. Ceramic cups can be cold so its' best to use a cup that is more temperature neutral, like styrofoam or paper.