The string will stretch a little when it is new, but should settle down after you use it a few times. As was mentioned, the string tends to be a little shorter when you first re-string it, so if I'm going to check my brace height, I do it after I shoot the bow for a while. If you're going to take the string completely off the bow, you can loop the ends together in such a way that they don't untwist. It is a good idea to check the brace height from time to time, because you may need to add a twist or two. If the brace height changes very much after the string settles in, it probably means something not good is happening it is a good time to change the string.