A phase index is a small exact ledger, not a full reconstruction. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A phase index can pin position
The phase index is 2 per metre. Positions 0, 1, 2 metres give ticks 0, 2, 4.
2⋅2=4
This is an address ledger, not reconstruction
The checked claim is the position-to-phase ledger. Fourier reconstruction stays outside this toy model.