Maybe a typo for 1/16" (0.0625")?
Anyway, the measurement need to be made at least w/feeler gauges between the quench band and the straight edge across the deck, spanning the bore. If you use a ruler, tip it up on its short edge, not laying flat where it can bow.
Below the piston is a true flat top. You would do the same thing except measure to the quench band of your piston: