A known training peak calibrates a linear detector scale. 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 known peak fixes the scale
Known ratio 4 appears at position 8, so the scale is 2 position units per ratio.
scale=8/4=2
A measured position maps back to a ratio
Position 12 maps to ratio 6. No peak fitting or database search is modeled.