It's easy to take a go gage, any go gage, multiple go gages and use that one gage to cover from go +/- .0000" to field, usually +.0100" accurately. Use shim stock in various thicknesses not tape. A small piece of shim stock and a dab of grease to attach it to the base of the gage works great. I would get a piece of .0020" thick stock. Five pieces the same thickness will get you to +/- .0010" on the headspace. Any finer measurement is best left to micrometers and means nothing to all but a few. Also remember not all gages will measure the same. If you want to verify your gage get a ring gage the appropriate diameter to match the datum line diameter, have it surface ground to get a sharp corner and use a surface plate and height gage. Pretty simple.