BMC timemachine Mode D'emploi page 7

Positioning
To take those measurements, the easiest way is to place your bike on a even, horizontal ground and lean it against a vertical edge (for
example a corner of a wall, a pole or a door case) and align it so the edge is centered on the bottom bracket axle.
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Then follow this procedure (picture):
- Measure the vertical distance between the BB axle center and the ground (BBH).
- Measure the vertical distance between the ground and the top of the saddle (VSH).
- Measure the vertical distance from the ground to the middle and upper surface of the bar pads (SP).
- Measure the vertical distance from the ground to the center of the handlebar clamp (SS).
- Measure the horizontal distance from the edge your bike is leaning against to the center of the pads (RP).
- Measure the horizontal distance from the edge to the center of the handlebar clamp (RS).
- Measure the horizontal distance from the edge to the tip of your saddle (SSB) (Figure 5).
SSB
RP
RS
Figure 5
Example: how to measure the reach on your old bike