Infrared thermometers usually have to be calibrated. When you get them, they measure radiation as if the surface they're measuring has emissivity ratio of 1 (black body radiation - which means all of the bodies heat is radiated out). If you know what the actual temperature is, you iteratively change the emissivity until you get the correct measurement. When you measure a different surface, you'll have to repeat the same process though.
Cc: /u/AspGuy25
shlepky t1_j5p2k9q wrote
Reply to comment by aspheric_cow in Why does hot air cool? by AspGuy25
Infrared thermometers usually have to be calibrated. When you get them, they measure radiation as if the surface they're measuring has emissivity ratio of 1 (black body radiation - which means all of the bodies heat is radiated out). If you know what the actual temperature is, you iteratively change the emissivity until you get the correct measurement. When you measure a different surface, you'll have to repeat the same process though. Cc: /u/AspGuy25