Did you test them against a known temperature and salt slurry??
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.