"...why they spell it "gage"..." It's American vs The Queen's English. snicker.
Been loading match grade ammo for 40 some years without any of the current measuring tools. Never seen any need for any of 'em. Digital Verniers are easier to read though.
Wilson keeps calling their gauge a head space gauge too. It's not. Cartridges do not have head space.
It's faster to lock your Vernier calipre at the max case length given in your manual and use it as a case length gauge.