That will be a hard thing to do, short of removing the boat of the water, getting at least 2 scales at the same time, and what not.
Assuming the boat is dry in land.
Assume that the CofG is somewhere near the end of your keel, or slightly aft of the mid part of the keel. or thereabouts. And anywhere from one foot to 2 feet from the bottom of it, and in the bottom if you have a led keel