Parallax Error

For general hunting purposes, parallax error is most critical at under 100 yard distances. And, this is why most rifle scopes are set to be parallax error free at 100 yards. At under 100 yards, wild game are large enough that parallax won't throw you too far off your aiming point. Beyond 100 yards, the error is simply less for the difference in distance.

Adjustable Parallax scopes have a lot of adjustment under 100 yards but just a little as range increases over 100 yards. So, if your scope tests parallax error-free at 100 yards, it is going to work just fine for probably 95% of all hunting situations. But, if it shows a lot of parallax error at 100 yards, it is simply not going to shoot accurately and reliably.