Old style thermometer vs. combo thermometer/hydrometer

[dyoungen]

I have an older incubator that I've been using for a number of years with some success. I bought an old style thermometer a few years ago. the glass thermometer with the numbers on a plastic sheet behind it. This year I bought a combination thermometer hygrometer. I've got the thermometer and combination layed on top of the eggs so I can see it thru the windows. The thermostat I've got set at 100 degrees and having good success hatching chickens and guineas. When I got the combo thermometer/hygrometer I velcroed it next to the older thermometer. The older thermometer reads"100 degrees" and the combination thermometer/hygrometer reads "102 degrees" . The older thermometer olny goes down to "70" degrees so I can't tell if it's right or the comco is right. Any ideas to tell which is right?

 

[ChickenCanoe]

Compare them to an oral thermometer which is more accurate.
Most thermometers are only supposed to be accurate to within ± 2ºF. and usually are farther off than that.
I use these. Both extremely accurate - guaranteed.
https://www.brinsea.com/p-394-spot-check-digital-incubator-thermometer.aspx
http://www.thermoworks.com/products/low_cost/rt301wa.html