Does anyone have access to a wet bulb globe temperature monitor?

I've been curious for a long time, since the NOAA's heat index only begins at 80°F (27°C), whereas I've been in trouble from the heat more often when the temperature has been in the low 70°s F, or even the high 60°s, but with humidity high enough that sweat evaporation is minimal. I'll actually experience less heat stress if I run in the hottest part of the day when the humidity is lowest, provided the humidity drops below 75% at that time of day - which lately it hasn't been doing.

I might just have to get an inexpensive monitor just to satisfy my curiosity.