Quick temperature question

[Huntmaster]

You should be ok.

 

[My15Ducks]

Last night I checked my incubator with the oral mercury thermometer and it said it was 100.2 F. So I lowered the temperature, waited, checked again. 99.6 F. I checked again this morning and it’s 100.2 F again!!! I don’t know what is causing it to go up