To expand on the sag issue, it will help to put a bit of tape on a part of the frame directly above a similar bit of tape on the CARC. Draw a horizontal line on each bit of tape. This gives you a very accurate reference line for both the moving and stationary marks. Then use a metric tape measure because the graduations are usually easier to read and digest. I use a wheel chock to hold the bike upright but still need an assistant to read the tape. Remember to bounce the rear a couple times so it comes to a 'natural' stopping point...then measure.
Growing old ain't for sissies!