Easy solution, Calibrate the thermometers. Like they have to do monthly in catering with food temperature probes to ensure accuracy.
To calibrate - have crushed ice and boiling water.
The crushed ice should be 0 degrees centigrade and the boiling water 100 degrees centigrade.
Let the ice melt a little so you have some ice water.
Centigrade is obviously easier with the numbers being so simple.
But convert to fahrenheit if you prefer.
Also a laser pointer helps ensure your pointing at the exact spot you want to record.
This way you know which one is accurate. even if neither are you will at least know how many degrees they are out by.