Originally Posted by
ducati hyp
That would be hard to do while the chain is on the bike and if done off the bike it would be tough getting good tension on the chain..
It's easy on the bike. The lower run of chain almost always has at least 12" of unobstructed length to measure and the rear derailleur's spring provides some tension so you get an accurate measurement.
Shifting the chain to the largest chainring and smallest cog will give the longest free run.