May have worked to long.
Any of the newer thermometers will work, even the little $10 from Harbor Frieght, which I have one, and the bigger, more expensive one, which I use as well.
Both will do the job, brand is not important, that's just marketing of the same tool with a name on them.
Learn to "look into the paint film" with a good magnifer, is you see "bubbles", or deep cloudiness, you may have some deep damage.
One wipe or such with a polish should and usually, will remove the "water spots", but if after that, you see the afore mentioned conditions, it's usually the dreaded "etching", which is the breaking apart of the resin system of the paint film (binder/film former", which is what keeps the paint film together and produces the nice "gloss" everyone wants to see.
(by the way, those "acids" that caused the problem will not be removed by clay or buffing, so once the surface is exposed to more water(oxygen molecules/oxidizer) and some heat above about 70F, the acids reactivate and start "eating" again. Even worse in large city's where it is warmer and have a pollution problem of "ozone", which is a more active oxidizer than oxygen)
Grumpy