Some wonderful stuff!
I have to ask. Were these simply precision/adjustable gauges that helped finesse a sight-setting and return to a 'recorded' setting ... or ... do some models remain attached to a sight to add micro-adjustment for elevation?
The micrometer is placed on the sight and used as a precision gauge to make small elevation changes between shots. After making the sight change the binding screw on the elevation slide is tightened and the micrometer is removed and set aside.
The earlier square imported version has no click adjustments but has a vernier scale on the side. The later O'Hare features click adjustment detents which is the "easiest" to use and became "the standard" for riflemen shooting the M1903 on the range.
The micrometers were easily lost on the firing line. [smiley=sad.gif] The standard remedy was to tie a spare GI boot lace to the knob on the micrometer and secure the other end of the cord or lace through a button hole on shirt or jacket. Sometimes seen in vintage range photos if you look close.
