With an alt-az telescope the field rotates as the telescope tracks, and the instrument is rotated to compensate for this by a two motor instrument rotator with integral cable wrap. Unlike the Cassegrain rotator the Prime Focus rotator only has a travel of 358 . This means that it is not possible to observe at certain position angles, and that extreme care must be taken when starting an exposure that the turntable will not run into a software limit before the exposure ends. Users are recommended to: (A) use Chris Mayer's PLANETS program, which will tell you if and when a given source will reach a wrap limit. PLANETS is an Xwindows application that runs under VMS and Motif, and is useful also to see if and for how long a planet or other source is visible from a particular observing site. (B) check on the TCS display to see the time to reach wrap limits.