I’ve found the forehead thermometers inaccurate - they always seem to read low. Flushed kid, hot to the touch, 98.0 F. And Ebola virus is present in sweat, in every body fluid.
An external thermometer is always going to read low. Rectal is best measurement, oral measurement is good.
This method isn’t about finding a perfect temperature measurement, it is about RELATIVE difference. Ebola temps run to 104F, normal is 96 F. The forehead instrument accuracy may read a little low...but it will quickly spot a relative difference of 8 degrees F. Quick relative difference is what you need for screening hundreds of people quickly.