Potentially Dumb Thermometer Questions

[Zephyr]

I have an topic related question.

i have 3 thermo meters.

1 thermometer of the thermostat.
1 little thermometer with 2 probs.
1 temp gun

When i check the tempratures in all 3 machines ( even the 2 probes of the little thermometer) give a different temp.

At at first when i didnt have the temp gun i just took the average of the 3 probes and took that as the actual temprature, but now i also have a temp gun who gives me another different temp. I am not sure what thermometer to believe. Any one that can tell what i need to do to know what thermometer is right?

Test them all on boiling/freezing water? Water boils at 100 deg C (212 F) and ice water is about 39 deg F.