So I want to get lower but my pads are bottomed out: P5-3 with no steerer tube spacers and Ventus II LTD with no pad spacer. I measured the pad stack from the bottom of the steerer tube clamp, at the mid point, up to the top of my pad at it's lowest point. That was around 60mm. Assuming they are compatible, I could get a PD Ultimate Stem (12.5mm stack) and Pro Missile Evo bars with under-mount extensions (20mm stack) to get lower but I've started entertaining a new frame. In my bike fit comparison spreadsheet I just used the published stack height for my 58cm frame, 559 mm, and added the 60 mm to see what my baseline is. Out of curiosity I measured pad stack and it didn't add up so I measured frame stack. Bike is level within 2 mm per measurement from floor to skewer center. I measured from floor to the center of my cranks and then from the floor to the bottom of the dust cap, at it's center. The difference: 568 mm. 1 cm different from the published value. Is that normal? Does Cervelo measure differently than their diagram suggests?

Generally do the measuring points for manufacturer frame stack/reach vary? Now I'll be paranoid that if I order a frame based on published measurements, it won't be right.

tldr: I measured the stack on my 58 cm P5-3 and it appears to be 1cm more than advertised. What gives?