Have you ever wondered what those two lines of tape are doing on the jumper ring schooling standards at some horse shows?
Those lines are measured and taped by the show steward to make it easier for both riders and stewards to ensure that the height-related rules are being followed.
The lower line is put at 1.30m (4'3") and the higher line is at 1.60m (5'3"). For many, these heights will never be jumped in the warm-up ring anyway, but certain tape-related rules might still apply and the tape can help you keep track of how high you're jumping.
While the Canadian and American jumper warm-up rules do differ slightly, they are the same with regard to the tape with one exception. The Canadian rules do not allow riders to jump more than 10cm higher than the height of the competition currently taking place in the show ring. This means that if the class is running at 1.20m, the warm-up jump is only allowed to be adjusted up to the point where the top of the highest rail is even with the lower tape. Even for lower classes, knowing that the tape is at 1.30m can make it easier to estimate the height of any jump that is set.
The role of the higher tape is to set a limit for how high the horses are permitted to jump in the warm-up ring. Rails may not exceed the height of that top tape (1.60m) for any competition.
The lower tape helps to enforce the rule stating that a minimum of two rails must be used on the take-off side for any jump at 1.30m or higher, with the lower rail always staying below 1.30m. This is a way to avoid overly airy fences that would be unfair to the horse.
In addition, trot/canter/placement poles can only be used when the jump is set at 1.30m or lower (therefore the top of the highest rail mustn't be higher than the bottom tape when using any rails on the ground except for ground lines within 1.0m of the fence).
The tape-related rule most likely to affect those jumping the lower heights is that the cups used to build a cross-rail may not exceed 1.30m. Because the middle of a cross-rail where it is jumped is much lower than the height of the cups, it's quite easy to approach the height of the tape when raising an X to anything more than a relatively low height.
For full warm-up rules, you can check the individual rule books: