Read this.. http://www.desertsharpshooters.com/m...incredload.pdf
It thoroughly explains how to properly do a ladder test, and will answer all your questions LD.
I would also like to add that in order to realize the benefits a ladder test provides you you have to be capable of shooting at least MOA, SUB MOA is better. If the best you can do is Minute of Grapefruit at 100 yds then youd be well suited with a middle of the road load from your manual of whatever powder and bullet is listed.
Please nobody take me wrong on this, not being able to shoot SUB MOA doesnt mean youre a sucky shot, being able to achieve consistent SUB MOA skill requires alot of discipline and tons of practice. 90% of shooters do well to shoot 4 MOA at 100 yds. Thats a group, roughly the size of an orange dome clay pidgeon.