Should I use the 6-inch or 2-inch globe?

The Globe part of the WBGT measurement calls for a 6-inch (15 cm) diameter hollow copper sphere painted matte black on the outside, or the equivalent. The standard sensor bar comes with a 2-inch globe for faster response time. The temperature of the 2-inch globe is correlated to match that of a 6-inch globe.  An optional sensor bar with a 6-inch globe is available, if desired, but is not necessary.

What is WBGT?

It stands for Wet Bulb Globe Temperature – It is a weighted averaged of the three sensors on an area heat stress monitor: the Wet Bulb, Globe, and Dry Bulb. The WBGT formula for indoor measurements is 0.7WB + 0.3G. The WBGT formula for outdoor measurements is 0.7WB + 0.2G + 0.1DB.