You can't really calibrate the ballistic reticles in scopes. Most of the major center fire rifle cartridges have similar trajectories, and the reticles in these scopes are based on a generic estimate of trajectory. Aiming points for most rounds range from 100 yds at the x-hair intersection to 500 yds for the bottom point. An extremely fast round would be zeroed at 200 yds for the first mark, up to 600 yds for the bottom mark. You can make the aiming points work for your preferred zero range, you'd just have to shoot at long distance to see the yardage for each mark.
Honestly, I've not read too many positives on the Gameseeker scopes as of yet. I like to read the reviews at Midway USA to see what people think of products, and the reviews on the Gameseeker are probably 50-50 right now. They are an excellent price point for a ballistic reticle scope, but I think that the jury is still out on them right now. With the attractive prices you can find on Burris Fullfield's right now, I would spend the extra $$ for it, or for the Nikon's with BDC. I think you'd be alot happier.