Start at 25 yards to make sure you are on paper.

Move 25 yards at a time to ensure you are still "on target".

Set your cross hair at 100 yards (unless you prefer to "zero" at 200 yards).

I wonder how many rifles go into the field every year after being sighted dead on at 25 and considered good enough. Often because the hunter has no access to a 100 yard range.

Way too many I'm thinking.

Sighting a scope is as easy as how much time and effort you wish to spend taking benched up shots at various ranges. When you start seeing a trajectory then you have made excellent progress.

I wonder how many unzeroed @100 yard scopes are put on rifles that would shoot better with the factory sights. Then I think about the guys at the range who shoot AR-15s and AK-47s benched up on the the 25 yard target and never move to a farther target. (A lot of people spend money on overkill things they do not use to their full potential and would be better with something simpler.)