A standard cheap wally world thermometer works good for double checking. Sometimes the temp of the QF will get a little out of range so its hard to tell by touch whether its a little low or a little high. And as stated earlier,don't buy one with a beeper.lol I kept it in my sock to double check when I was in the toilet. A little too high blow on the sample for a couple seconds,too low rub your thumb against your pants and touch your thumb to the temp strip on the cup.