According to the cookbook, Grillin’ with Gas by Hank Hill Fred Thompson, and reproduced on Culinate:

“Judging the doneness of steak is not as much science as it is technique and feel.

“Poke your index finger into your cheek at mouth level. Then press your finger into the steak. If they feel very similar, that’s an indication of a rare steak.

“Touching the tip of your nose gives you the feel of a medium steak, and touching your forehead is a medium-well to well-done steak.”

Use a tip-sensitive thermometer and stick it in.