Thanks for the update Dave. Yeah, it's difficult to see the motor numbers without taking them out, well done for your perseverance! Unfortunately I don't have a C8, I've been looking out for one on and off but I have a 1981 C5 which used the same base as the C8 and it's not easy seeing them. Sometimes, there is a space between the first and second digits, sometimes not, I guess it depended on the chap stamping the numbers. The motor dates are quite handy for cross checking as they give the earliest date the scope could be built but there's a bit of an unknown in how long they sat on a shelf at the supplier or Celestron! So motors with a date of November 1974 tie in well with the serial number which shows your scope as being made in the 3rd quarter of 1975. As a kid, I spent many hours drooling over the orange tube C8 ads in Sky & Telescope and when I got back into the hobby I started picking up bits and pieces of the C8 history through the Classics forum on Cloudy Nights, including trying to make sense of the serial numbers. Also, bits have been picked up from Robert Piekiel's book, Celestron the Early Years, amd Rod Mollise's (Uncle Rod) blog and his Used CAT Buyer's Guide. The first ones, the tri-colours (the fork arms were a light greyish colour) which had a Velvet Tone finish, were just given a unit number and the very early ones (up to probably no 125 - they were originally made in batches of 25) had an axial focuser knob around the visual back rather than the offset focus knob that later C8s had. I think the tri-colours ceased sometime in 1972. Then they went over to the date style serial numbers but by the third quarter of 1977 they were getting up to no 9999 so for 1978 they changed to a 5 digit style of ?xxx Y (with the xxx unit numbers restarting), it's not clear to me yet whether the ? represents the quarter (which would limit them to 999 per quarter) or is the first digit of a 4 digit unit number. Also, it seems, based on serial numbers that I've seen, that the change from the sand cast mount (holes in the forks) to the die cast mount, occurred sometime in the first or second quarter of 1976. Then, sometime in 1979 they changed to a non-date specific serial number, which for C8s was 8xxxxx with xxxxx being a sequential unit number (C5s of the period had 5xxxxx numbers). At this time, the location of the Serial number changed from a plate on the base to a number on the secondary holder in the corrector. So, after 1979 aging a C8 becomes harder if there is no reliable evidence of the purchase date, although the motor dates can give a rough idea. James