Dressage: what are the rectangle letters for?

What the letters in the dressage rectangle are for

A, K, V, E, S, H, C, M, R, B, P, F, D, L, X, I, G–these letters are a real nightmare for every dressagist!
Those who practice this fine discipline, whether on horseback or with bindings, must confront these enigmatic symbols every day.

Dressage (from French: “straightening” or “training”) is an equestrian discipline that involves performing movements on a rectangular field measuring 20×60 meters.

Seventeen letters are used (twelve physical and five virtual), but for less experienced riders, the number is reduced to twelve (eight physical plus three virtual).

These letters are arranged at fixed distances and subdivide the short and long sides of the course, as well as the imaginary lines of the diagonals, longitudinal and transverse. They represent crucial reference points for “drawing” the movements to be performed by the riders, guiding their performance with precision.