I agree with Steve. A variable speed box is very important to those of us who don't have live musicians to work with. In teaching a new dance or figure I often slow the music down so all can get the figure correct and get where they belong in the correct amount of time. Later I usually bring the music back to tempo. However, it was mentioned earlier that many old recordings are faster than the tempo to which we dance today, and I concur. Also, some recorded strathspeys are painfully slow, so speeding them up is a help as well.