Check out this link:
http://www.opticsplanet.net/how-to-choose-riflescope.html
Repeatability
Good quality scopes are repeatable. That is, if you adjust your windage and elevation dials for point of impact at one setting, then move them around and shoot in different places, often in a square grid, then back to the original place, the point of impact will be the same as it was when you started.
Good quality scopes will also move the point of impact when you adjust your dials, without having to "settle in." That is to say, if you move your elevation dial up three inches, your point of impact should immediately reflect that.
Sadly to say, more often than not, lesser quality scopes won"t do this without shooting a few times first, to "settle in" the scope"s internal adjustments. Some people "tap" on their scope with a coin or cartridge case to help this process.