Ideally one would do the rolling test While Sitting on the Saddle and with any normally carried load on racks (back and/or front) handlebar or seatpacks, rack trunks, frame bags and etc.
Weight on the bike compresses the tire, effectively reducing the size of the wheel, wheel covers less distance per rotation.

Example (using nominally identical rims, tires, and pressures):

130 lb. Racer Boi, calibrating computer on 17 lb. Road bike carrying small seat wedge and 2 water bottles would have longest measured distance per rotation.

250+lb. Clydesdale, calibrating computer on 27 lb. Road commuter bike carrying a 17 inch lap top, Hard cover engineering school books, lunch, thermos of hot beverage, and etc. totaling an additional 23 lb. would get notably less measured distance per rotation.