What cartridge, bullet, velocity ?

Easiest and best thing is shoot at 200 yard dirt berm with your 100 yard setting. Note the strikes position vs targets position you have the answer 

Use something easily seen, orange clay target, tin can whatever and have an elevation reference point.  How high is a nearby  target frame, no frame use a measured 2x4 stake

Our club's 200 yard match with spotters we get zeros for new shooters in 3 or 4 shots. If the shooter does what he's told and knows how to adjust the sight.

Boats

Add more,

Shoot one shot it strikes "about" 2 feet low. At 200 that's 12 moa. Raise sight 12 moa.  2nd strike it's a "little bit" low raise 2 more moa. 3rd strike it's "real close" that's enough berm shooting .

Real close to what you want, go to a paper target shoot a group, 2 shots is enough, measure the center of impact vs Bull and make the precise adjustment, you'r home with the exception, bench and offhand zeros are not the same. Couple of MOA difference depending on the gun and how it rides on recoil.

Boats