There is no method for measuring a frame that's perfect, but the stack and reach concept eliminates the BB drop, STA and fork length as possible sources of error. If you once know what stack and reach that you need, then comparisons will be more accurate. providing that you know how to compensate for different stack heights.

I've never seen any brand fail to list the STA, which is necessary to figure the seatpost setback needed. Most people don't realize this, but Cervelo fibs about the STA. When the R3 first came out with it's ridiculously short 399mm chainstays, they still listed the STA as 73 degrees, It's easy to prove that the tire would hit the seat tube, if it was angled as 73 degrees, along a line through the center of the BB, but it is not. The seat tube is moved forward of the BB centerline and actually angled somehwere in the 71-72 degree range. The net result probably places the saddle somehwere near the position of a bike with a normal STA of 73 degrees. I owned one of these frames, but only long enough to ride it for 200 miles. It sucked, IMO.

After a few years of production, Cervelo came to their senses, lengthened the chainstays to a normal 405mm and changed the fork angle on the 51cm from 73 to 72.2 degrees, which pretty well duplicates brands like LOOK, who know what they are doing.