@grumpybozo @paul_ipv6 @ryanprior @ai6yr you absolutely can directly measure Wet Bulb Globe Temperature, you just need special equipment. I have this relatively inexpensive device, although I can't say how accurate it truly is: https://sperdirect.com/products/wearable-wbgt-heat-stress-meter-with-tripod-mount

You can pay this shop extra to certify the accuracy of each device, and although that would make it significantly more expensive, I'm kicking myself for not doing it, because I'd like to trust my gear more, given life-threatening danger.