I learned to put it in the frame/fork and measure distance from rim to blade/stay on each side with inside calipers. I then take its reading with vernier calipers to get a numerical value and adjust close to even before final truing. I do that with the wheels on the bike too, soon to be with dial gauges that attach to axle/QR by morningstar tools.
I like doing it this way. It makes sense to me centering the wheel with its mate.