A tiled optical scan covers repeated fields of view. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
One optical field covers the image length
One calibrated field covers 12 m.
Lfield=12m
Tiled fields multiply covered length
With 4 non-overlapping fields, the covered length is 48 m. No stitching or segmentation is claimed.