There’s a reliable and accurate index for the heat which can’t be measured by iPhones or Macs, and isn’t understood by many anyway.
temperature
Summer is allegedly coming: the season when your Mac could see its harshest use. Does yours get too hot?
My iMac seems to be running a bit hot. How can I check its temperature?
I am worried that our Macs may be getting too hot. How can I monitor them?
The Eclectic Light Company 