Scatter plots of wet bulb globe temperatures from the instruments versus the reference unit. A, General WBGT8778 Heat Index Checker (General Tools & Instruments LLC, Secaucus, NJ). B, REED Heat Index WBGT Meter (model SD-2010; REED Instruments, Wilmington, NC). C, Extech HT30 Heat Stress Wet Bulb Globe Temperature Meter (FLIR Commercial Systems Inc, Nashua, NH). D, QUESTemp° 34 (3M Detection Solutions, St Paul, MN). E, Kestrel 4400 Heat Stress Tracker (Neilsen-Kellerman Co, Boothwyn, PA). F, WBGT-103 Heat Stroke Checker (Kyoto Electronics Manufacturing Co, Ltd, Kyoto, Japan).