For me the key thing is that I do all measurements from fixed points. I have the bike on a level floor, with the rear wheel right up against a wall. I try to level the handlebars. I start by measuring from BB center to the floor and the wall. Then the center of the top of the headtube to the floor and the wall. Then the handlebar, by the stem, to the floor and the wall. Then I put the board on the saddle, check with a level that it matches the other bikes. Then I measure from the floor to the bottom of the board at the predetermined point, and then from BB center to the same point, and then from saddle nose to wall. I also use a dowel, which I put in the place on the hoods where your hands go, fix it in place with rubberbands, then measure from there to the back of the saddle.
Floor to BB center...
Here's the saddle height measurement. Sorry it's blurry, but I had to hold the tape measure in my right hand while trying to snap the pic with my left!
This shows the basic problem with measuring saddle height - different bikes have different seat tube angles. But if you set the saddle angles all the same, and the setback relative to the BB the same, you can measure the saddle height, from BB center to the same point on the saddle. I used the Ritchey as the standard because it's so conventional, and it's my most comfortable bike. I put that board on the saddle, with the back of the board even with the back of the saddle. Then I lined up the tape measure from BB center to the bottom of the board, with the edge of the tape measure lined up with the center of the seat tube, and then marked the point where it lined up with the bottom of the board.
I enter the numbers, in inches, into an Excel spreadsheet, in which I added formulas to convert inches to cm, and also to subtract some numbers from others to give me others - like (Saddle to Floor) - (Bar Top to Floor) = Handlebar Drop. Here's the Litespeed's measurements, with the measurements in inches on the left and calculated values in cm on the right.
Hope this helps!