Tiller check

Compare two photos of a bow

Trace the back and belly of the bow in a before photo (e.g. braced) and an after photo (e.g. drawn), and see where along the limb the depth, curvature and bending strain changed. Everything runs in your browser; photos never leave your computer.

Controls
Click
add a point to the active side (or drag an existing one)
Drag / middle-drag
pan · scroll zoom
Right-click
remove the active side's last point
Tab · b · l
switch side · back · belly
a · m · d
add · move · delete mode
[ ] · Esc
select previous / next point · deselect
Arrows
nudge the selected point 1 px (Shift: 0.5 px), else pan
Backspace
delete the selected (or last) point
z · y
undo · redo
e · g · f · r
edge snap · grid · fit preview · reset view

Before photo

Drop a photo here, or

Trace the whole bow tip to tip. Back = the side facing away from you (the tension side); belly = the side facing you.

Peak strain change

Left/right asymmetry

Depth consistency

Peak strain (after)

The bow

Hover to find a spot on the charts.

Before and after

Along the bow from the photo's left tip (0%) to the right tip (100%). Grey bands: tips, least reliable; the vertical scale ignores them.

Depth

Curvature

Bending strain

Change (after − before)

Δ Depth

Δ Curvature

Δ Bending strain

Sign: curvature and strain are positive where the limb bends toward its belly. Strain ε = (h/2)·κ, using the average of the before and after depth.