(“. . . a 20 x 24 meter egg.”)
Ride in an actual dressage arena—at least some of the time—if you have any intention to compete. This may seem obvious but despite all the diagrams and articles which appear, I keep running into riders who can’t make accurate figures. Sometimes it’s because they can’t steer their horses, but lots of times it’s because they don’t know where they are supposed to go!
This is not only a novice’s affliction. The same thing happens to eventors making the transition to the large arena at Prelim B. I will ask them where they cross the centerline on a 20 m circle or on a three loop serpentine and it’s amazing how many times they say (pointing) “right between those two letters.”
Or if they learn “two meters past the letter” on the circle at C, They somehow decide to also go two meters past the letter on the circle at B or E and end up with a 20 x 24 meter egg!
Graph paper is your friend. Lay out an arena on it where each square represents one meter. Drill into your brain that from X to I or L it’s 12, not 10 meters. And from C to I or from A to L, it’s 18 not 20. Then go out to your actual arena and with surveyor’s tape or stakes or cones mark those 10 and 20 meter spots on the rail. Learn them so well that even when they are not present, you see them in your mind’s eye.
Another thing worth doing if you have not completed a lot is when you get to the show (preferably the day before), go hang out at the arena even without your horse. Lots of PVC rings have four meter-long boards set on pylons. If this is so at your competition, there is likely to be an unmarked pylon sitting right there at each 20 meter interval just waiting for you to use it as your reference point.
This stuff is easy. It’s really less about geometry than it is common sense. Find the dots, connect them, and don’t needlessly throw away points that will help you climb the leader board!