Precision of Telescope Pointing for Outdoor Targets

The probable error of a single pointing (PEs) is measured for a single telescope with a variety of targets. This investigation shows that, although some change in PEs with distance does occur, the distribution of PEs as a function of distance can usually be neglected and a value of 0.62 second assigned as a practical average. The values of PEs for an indoor target usually show a small variation from one experienced observer to another, and from right to left eye of the same observer. There is also a measurable systematic difference in pointing between the right and left eyes of the same observer. In outdoor pointing a long period error or drift is usually superposed upon the short period errors.