When laser beam is reflected at the facet of mirror,
it will make different scanning angle caused by
length of facet (number of facets).
Facet to facet angle of 6 facets mirror as shown on the left is 60 degrees. When laser beam is reflected on the facet, scanning angle will be 120 degrees. It is considered pretty wide in actual use.

(deg)
MIRROR FACET DIVIDED ANGLE SCAN ANGLE ANGULAR TOLERANCE
5 72° 144° ±30"
6 60° 120° ±30"
8 45° 90° ±30"
10 36° 72° ±30"
12 30° 60° ±30"