When you are competing over fences, the number should be centered in the middle of your back. In an under saddle or flat class, enter the ring with your number centered and then adjust it to one side or the other before the class begins. If the judge is sitting outside the ring, she will most likely ask you to move your number slightly to the outside. If she is standing inside the ring, she will ask for it to be moved slightly to the inside.
Moving your number slightly is very important. The judge must be able to take a quick look at any horse in the ring, and there is not time for her to watch you long enough to try to catch a glimpse of your number as you go around a corner. When you turn your number, make sure that you don't turn it so far that your arm covers the number!
The string that you should use to tie the number around your waist is generally a dark shoestring, available at the show office when you pick up your number.
There is a definite wrong way to thread your number; passing the string over top of the number is a big no-no:
There are two possible correct ways to thread it. One way allows the number to move along the string, which is useful if you hide the knot in a buttonhole on your jacket, making the string itself impossible to turn during a flat class:
My preference is to thread it so that the number is centered on the string and cannot move. This is done by first threading it through as seen in the two photos above. The next step is to ensure that the number is centered. This can be done either by holding the two ends of the string up together and moving the number until it hangs parallel to the ground or by stretching the two ends of the string out together and measuring by eye:
The next step is to then take each end of the string and thread it back through the hole it originally came through (in the same direction):
This creates a tight loop of string around the cardboard at the edge, keeping the number from sliding along the string. After securing both sides, the final result should look something like this: