manual for commanders of infantry platoons. - US Army Combined ...

~M~ASN~tTA POR;3t~ ~~CO1M&TMADI~ ~S OF :'INF;ANTRY. PLATOONS. 119
the othrer 'eye. Slight rotationsx of the per~iscope ab~ou~t its axis
makres possible, byi groping, the superp~osition of the two fields.
The relief of features t~hen suddenly becomecs extrazordinary andl
different foreground~s detach t~hemselv-ersfr.oml each other wvithi
igreata clearness. Rnecognition of mroving 01)jects onl the horizon
is. also: facilitated~.
3. Comparss-Th·e blue end of the needle indlicates iwh may.z~
n~etic nzorth.. Compasses~ are graduanted fr~omi 0" to 3d()" (or
from 0 to 400 gradces, or fr'oml 0 to 6,400 mlils) in~ tbe d'ir~ection o~
the fig~ures on a clock. The line 0-180 (or 0-200? or 0 3,20·0, de~
pending on the type), w-ihich generally b~ears5the iildications N~. S.,
becomes the geographic north and southl line when the blue
needle point is (for PaiI~is) 1.370 (15: g1:rades or 240 miils) to the
left of the 0 of the compass. Thle conmpass mzost w-idely ulsedl is
one writh a. needle i1- inches lonlg andth l-e bottoml of wlhich,
moving with slight friction .on the rest of the box, carries a
large black direction arrowi~,codncentric w-ith the magnetic nee~lle.
There is added'a sm~all cop~per l~rotraetor. The precisioni of the
mneasuremzentf of angles is in proportion to the length of the
needle. The needl~e is influenced by the pr~esence of iron
(helmet). i
To orient a mnap.-Place thne compassr on the mapg, tile 0-180
line on the meridia~n. Turn tile manp car-rying the comnpass until
the blue point markl'ls the proper d~eclination. Thle mnap is t-hen
oirientedl.
If, inllstea(1 of mkeridia~ns being mark:·edl on t-he ma~tp, an arrow~T
indicates the true northl (N.~ G.), place the compa~ss so thac't the
0-180 line! coincides wTith~ the d'Iirection of the arrows. Trnr l
t-he mapD bearing thle compass until thle lleedlle indlicate~s thle
d~eclination. If thle margnetic north is given, place, ltile 0-180O
l~ine coincident in dlirect-iont wTith it andl turn thle mapl wLith the
compass' till the needle is a~t 0. Tlhis dispenses; w\ith thle neces­
~it;y for laying off the dleclination w~it~h thle needile, thle (iodlinetion
varying wititl the lo'cality.' (Tr~anslator's note: TIhe ab~ove
w~ill only give correct r·esults wrhen the (leclinationlaid off is the
true dleclination of the l~oca~lit-y in wrhichl the mnap is being used;
or, int the last: case, wihenrtile ma~gnetic N, and~ 8. line indicattedt
B~n tile. map 'is the true magnetic 'meridia~n for the place in; w~hich
the map is uxsed.)