Eric, Well done! It would be interesting to see a "dust closure merit factor", the ratio of "dust accumulation avoided" to "telescope time lost", plotted against closure level. Would you calculate the merit factor from the data used to plot Figure 2 on your web page? I'd like to know if there is a peak in the merit figure, i.e., a closure level where you get the most protection for the least lost time. Jon APO APO APO APO APO Apache Point Observatory 3.5m APO APO APO APO APO This is message 191 in the apo35-general archive. You can find APO the archive on http://www.astro.princeton.edu/APO/apo35-general/INDEX.html APO To join/leave the list, send mail to apo35-request@astro.princeton.edu APO To post a message, mail it to apo35-general@astro.princeton.edu APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO APO