On Tuesday, October 16, 2018 at 1:03:31 PM UTC-4, Phil Hobbs wrote:

Your accuracy requirements aren't high, then. A shiny metal surface can
easily show up as 90% room reflection and 10% surface emission. A bit
of tape will reverse those numbers.

Perhaps not. 90% of the use is to verify that I am not looking at a freeze-out on an AHU coil or at the discharge temperature of a chiller. And in such cases, it is pretty much go/no-go. I am not the mechanic, but I have learned over the years that "trust but verify" does not only apply to the former Soviets.

But, for 10% of the use, it is to let office workers, docs or other staff know the temperature in their space. The docs have, on more than a few occasions, pulled out a thermometer of their own - and so far, they and my little heat gun have agreed.

On rare occasion, I will use it at home to verify radiator temperature against the gauge on the boiler, or to look for hot-spots in some bit of audio or radio equipment, or other. And, if one tube on an output pair is acting differently from another, I understand I have an issue.

Peter Wieck
Melrose Park, PA