Thermometer confusion

I bought some stick thermometers and I have some digital ones too. I just calibrated my digital thermostat with my digital thermometer with a probe (ice method). I had to adjust the thermostat down .6*c to hit 0, and noted my thermometer read 33.1*f (so one would think to get 99.5*f it would need to then read 100.6*f, right?) - only once back in the incubator the thermometer reads 98.8*f... now, the stick thermometer by the thermostat probe reads 99.5*f, what is up with the digital one? I only have the probe for it run in and it sets on top of the incubator next to the thermostat. I am so confused.