If the rollers wear by the same percentage as pin to pin distance stretches, a simple chain checker will give the consistent result.
Chain checkers only see the "slop" in the two rollers they are inserted between, not every roller in the span between them.
So if your tool measures 6 links of unstretched chain, it'll see 3 inches plus two roller slops.
And if your tool measures 12 links of unstretched chain, it'll see 6 inches plus two roller slops.