Finding Center of Gravity in Backpack

What I am trying to solve is that when we go throghhiking / multiday hiking, we will carry a lot of stuff in backpack(around 12kg ~15kg). If not pack properly, the backpack will pull back, even worse the muscle will get hurt. Some even have hip bruise.

By get the pack right, you can have a more comfy trip, and best of all, save some bucks to (not) buy a new pack (if you are lucky)