An example of this would be the 25 yard zero. Lots of us have trouble finding a full hundred yard range that is accessible. Applying a 25 yard zero to our weapon is sometimes the quickest and easiest to accomplish. That being said, you need to understand what YOUR zero applied to YOUR weapon will do at different known distances.
With a 25 yard zero ( point of aim = point of impact on aiming point ie center mass) applied to the weapon, sighting in on a target at a known distance of 100 yards - holding the aiming dot center mass on the target, what do you think the round is going to do? Do you have a good idea? About how much do you need to hold over or under for a given range?
In this case Holding a 25 zero center mass on a target positioned at 100 yards will give us a strike located high, approximately 6 to 8 inches above the dot which was held center mass. The strike of the round will be almost in line with the clavicle .
These are all questions you should be asking yourself. When you are given the opprotunity to train on a range or you are lucky enough to have access to ranges well beyond 100 or 200, get out and prove to yourself what hold over you need to maintain in order to place the strike of the round in a place of your choosing.
Bellow are diagrams to help you visualize the type of zero your weapon has applied over differing known distances. The diagrams are not drawn to scale. The weapon will maintains the given zero (i.e. 25, 50, 100, 200,300 yard zero) through the range of known distances . The aiming point is constant, in this case it would be center mass each time.
Note how the strike of the round travels at certain distance. These are the factors that you will file away in your mental tool box and draw upon each and every time you pick up your weapon and train. If you can't remember; take a piece of Rite In Rain note book paper and write down your known hold over or hold under at given distances. Tape that to the stock of your weapon, in a place that is readily available for you to reference.
We don't have to memorize everything right off the bat. Over time through repeated proper training you will engrave the technical information into your subconscious. Until that point, cheat. No one is giving you bonus points for taking the high road. "If you aint cheet'in, you aint try'in".