How to use a single caliper truing stand (vs dual caliper)?
When truing a wheel (such that the rim lies in a plane perpendicular to the axle) it is only necessary to measure against one side of the rim, as rims have a uniform width around their circumference (assuming there are no dents in the sidewall.

The other aspect of wheel geometry is correct dish (rim lies in a plane exactly halfway between the axle shoulders). Another question here indicates that the Park TS 2.2 needs calibrating to achieve correct dish. I believe most wheel builders use a separate dishing tool to ensure dish is correct.