I always trust my mercury thermometer, and my analog (alcohol)
Brinsea thermometer, I use digitals too, but ALWAYS in conjunction with trustet analog thermometer.
A tip for cheap and decent analog thermometer:
Try
Walmart aquarium all glass thermometer (pet section) Less then 2 bucks. Some of them might be off about 1 degree, so what I do I either take trusted therm of mine to the store, compare and pick up one showing same reading than mine.
Or you take a look at all of them on display, and pick up one which reading identical with most of them.
Exemple: assume there is 5 of them reading 69, 70 70 71 70 F (likely inside store temperature) I pick the one reading 70.
I found theese are good and reliable thermometers if you pick a good one, even if it is off 1 degree or so and you are aware of it, just take mental adjustment.
Can't beat the price. I use them in conjunction with my merkury or
Brinsea to spot check the temp in my home made cabinet style bator.