We had recently purchased a turkey breast. Included was a pop-up thermometer. I don't use them as I have several reliable & accurate Thermoworks thermometers I use.
I decided to check the pop-ups accuracy using a saucepan filled with water over a small keep warm burner on our gas range. The pop-up was held @ its base with a pair of long small point tongs. The
temperature monitored with my Thermopen's tip next to the base of the pop-up. The small burner allowed me to control the rise of the water temperature.. The pop-up popped @ 182º, 17º over the
165º done temperature.
It's hard to fathom someone relying on a pop-up to perform a proper cook. If not constantly monitored, the final temperature could be high. Then there is carry over to consider.
I realize this test was a sample of one resulting in more of an interesting result rather than several tests that would show either there was consistency or not & just how accurate these pop-ups are.