A machinist would put the bearings and spacers in, and install main cap, then measure with a bore guage and micrometer. Afterwards, then measure the crank with the micrometer or veneer calipers.
The at home method would be to install spacers, bearings, and crank, but use plastiguage.
Spacers would be a one time buy, but might have to buy different bearings if the measurements aren't right.
