Originally Posted by
CliftonGK1
Digital calipers.
Seriously, everyone should have a pair in their toolbox. They're cheap as hell now; you can get a pair for under $30 at Home Depot, or under $20 at Harbour Freight Tools.
Or stop being lazy and learn to read standard calipers.
Measuring a seatpost diameter (or much of anything on a bike) does not require a digital caliper. And if you really needed to get exact measurements, you would get a dial caliper.