Hi Chuck I was thinking about Tony's idea of the multiple and it occurred to me that there was an issue. We've been thinking of the flashes as instantaneous strobes while they have duration. This would, as you state, cause a loss of contrast. This would tend to overlap the dots and white space of adjacent dots. This would indicate that a continuous 400 dots would most likely work poorly. Still, the spiral method should work fine, with just as much contrast as the single row method. One could use the original size dots and spacing. So, I feel that the fellow was incorrect that such a strobe disk could not be made for exact 45 RPM. Now, looking at the 78 RPM problem, the task seems more difficult, for both 60Hz and worst for the 50Hz. Still, three or four spirals with the correct spacing would be enough, even if it didn't come out to a nice integer. Dwight _________________________________________________________________ Share life as it happens with the new Windows Live.Download today it's FREE! http://www.windowslive.com/share.html?ocid=TXT_TAGLM_Wave2_sharelife_112007