The M1902 rear sight is a tangent type with better windage adjustment.   The elevation is locked with a clamp slide.  The sides of the "ladder" and the clamp are serrated to help prevent the elevation clamp from moving as the rifle recoils.  The size of these serrations determines how fine you can adjust the elevation, and the sights were made with two sizes of serrations.  I believe they are .080" and .040".  The coarser serrations (the larger) limit the precision of adjustement to 25 yards on the elevation scale.  The true minutes of angle varies with where you are on the elevation scale, so it's not very convenient of you are shooting something other than the ammunition that the sight is regulated for ... the 220 grain FMJ at about 2000 fps at the muzzle.  The finer serrations allow adjustment to 12-1/2 yards, but it takes some dexterity (and practice!) to be able to utilize that precision.   

The windage is a moveable carrier on the rear of the "ladder".  The carrier is moved by screw threads with a knurled thumb screw.  There are markings in the fixed and moveable parts of the base for reference.  These "points" are equal to four minutes of angle on this sight note the difference from the M1901 sight.  Since the adjustment is driven by a screw, it has better precision and repeatability, but all the sights I have seen have some backlash in the screw, so the shooter will need to pay attention to when the carrier actually starts to move.

Advantges and disadvantages?  See Part three ....

Resp'y,
Bob S.