So the question came up: “Exactly what happens when one of those things gets wet?”
Which obviously requires an experiment:

That’s the mis-cut top deck revealing why GRBL really needs four digits after the decimal point, but, other than that, it’s perfectly representative of the genre: heavy paper, good ink, nicely laminated in plastic.
Prediction: water should seep into the paper, dissolve the ink, maybe delaminate the plastic, and generally make a mess.
Which is exactly what happens:

User Advisory: your shiny new Homage Tektronix Circuit Computer is not waterproof, so don’t use it in the sauna!