With smooth-bore arms of short range, the soldier needed little more, in the way of sights, than the rough equivalent of the dispart of cannon, viz.
Guns without dispart sights cannot be layed at elevations below the clearance angle.
This was of wood; the third sight, also of wood, was for guns without a dispart patch, which consequently could not be layed at elevations below the dispart.
If the dispart sight were EarlyTangent being used, the sighting radius would be OD, but, as Sight.
D is the dispart sight, S the tangent sight, A'DS the clearance angle.
In the case of most guns it was used in conjunction with the dispart sight above referred to.
At greater elevations than this the muzzle notch is used; to align on the target at lesser angles the dispart sight is so used.