3 Thermometers, 3 very different temps, which to trust?

[Shalom Farm]

I have an incubator which I know to be slightly off. The thermometer that is built in will read 93F, While a digital Thermometer will read 101.1F. That's an awful big difference! So I added in an extra thermometer in the same place and height that wasn't digital, it was a food thermometer. Its reading 97F-98F on average. No eggs in it of course, but which can I trust? I have only one last thermometer that came with the incubator. I haven't taken a reading on that. The eggs come in tomorrow, so I need to get my final settings done tonight so I have a day to monitor it "at temp".

Which one is more trustworthy?

 

[NikonD2xer]

you need to calibrate your thermometer.

you can look here to find out what you need to do

http://seattlefoodgeek.com/2010/09/how-to-calibrate-your-thermometer/

 

[aart]

Tips on checking accuracy of thermometers and hygrometers:

The thing you want to do is check that any of thermometers and hygrometers are correct by testing them against a known criteria.
Comparing devices is useless unless you know how accurate any of them are.

I used a candy thermometer tested in boiling water and noted how far off 212 degrees it was...or whatever temp water boils at your altitude.
You can check your boiling temp at altitude here.
Then put the candy thermometer and 3 others in the incubator during the test run and compared them all, noting any differences.
I made a chart noting all temps and made notes about if this one reads this temp it is actually that temp.

Hygrometers can be tested by putting 1/2 cup salt and 1/4 cup water in a dish or jar and mixing it to a slurry.
Put the salt slurry jar and the hygrometer next to each other in a sealed plastic bag.
After 8-12 hours the hygrometer should read 75%...again note and differences and you're set.