Measuring "Drop at Heel" is the distance described, where you measure from a line extended from the top of the barrel, down to the heel of the stock( or top of the buttplate.)
There is a second measurement for "Drop". That is "Drop at Comb". Its done by measuring down from that line along the barrel to the point of the comb closest to the wrist of the stock. Some builders refer to that part of the comb as its " Nose", largely because of the similarity of the shape of the forward part of he comb to the human nose.
In most Traditional MLer stocks, the Drop at Comb will be shorter than the Drop at Heel. When building a stock, you want to take into consideration the distance from the center of your pupil, to the underside of your cheekbone, so that your eye will naturally align with the top of the barrel,( or sights on a rifle) when you mount the gun to your face.
This is also the time to determine how much Cast-off, or Cast-on for left handed shooters, you will need to help the eye align with the center of the barrel. The eye is the "rear sight" on a shotgun or smoothbore, so positioning the eye by properly configuring the stock is important. :hmm: :thumbsup: