Before you change a stem
A geometry match is a starting point, not permission to install a part.
Check the measurement convention
Total steerer rise is measured along the steerer to the stem-axis center. Include the headset cover, spacers below the stem, and the stem clamp-center offset. For a symmetric clamp, the last term is half the clamp height. Do not add spacers above the stem.
Check the hardware
Verify steerer and handlebar clamp diameters, stem orientation, minimum steerer engagement, manufacturer spacer limits, carbon-steerer restrictions, cable and hose length, routing, and torque instructions. Proprietary and integrated cockpits need manufacturer-specific checks.
Record a baseline, then change one thing
Save the reference plan or download its JSON before exploring changes. The trial buttons change only the candidate stem length and angle, keeping entered steerer rise fixed. Their remaining offset is shown in millimeters. Use Undo immediately to restore the prior setup.
Take an auditable plan to your fitter
Print or export the measurements, reference and candidate coordinates, model version, and assumptions. Mark values you have not verified. Small numerical differences can be smaller than your measurement uncertainty, and a near-zero offset is not a comfort or safety rating.