Body condition score (BCS)
A hands-on scale, usually one to nine, for judging whether a pet is too thin, right, or overweight — more useful than the number on the scales.
Weight alone says nothing without a frame to compare it to; a scoring scale gives you the frame. You feel for the ribs under light pressure, look down from above for a waist, and look from the side for a tuck behind the ribs. Ideal is roughly the middle of the scale, where ribs are easy to feel but not to see.
It is worth learning because it works on any breed, at home, without equipment, and because it catches gradual gain that a yearly weigh-in misses. It also settles arguments about feeding amounts faster than any chart: the guideline on the bag is a starting point, and the dog's own body is the correction.