140 U. S. COAST AND GEODETIC SURVEY 
sary that the zero hour or beginning of the day shall correspond to the 
double hour mark on the marigram. This adjustment may be accom- 
plished by moving the hour hand on its shaft after releasing its set 
screw. A finer adjustment may be effected by changing the position 
of the contact spring back of the dial face. 
406. Minute-hand adjustment.—This is to be adjusted to read zero 
on the exact hour indicated by the hour hand and the closing of the 
electric circuit for the hour mark. The adjustment may be accom- 
plished either by moving the minute hand on its shaft after releasing 
its set screw or by means of the releasable gears on the main vertical 
shaft of the dial case. The adjustments just described are those which 
need be made only occasionally. Other adjustments are taken into 
account each time the machine is set for a station. 
407. Setting predicting machine ——The time indicators on the face 
of the machine are first set to represent the exact beginning of the 
period for which predictions are to be made, which will usually be 0 
hour of January 1 of some year. The hour and minute hands should 
always be brought into place by the turning of the operating crank in 
order that the adjustment of these hands relative to the electromag- 
net circuit may not be affected. The date dial may, however, if 
desired, be set independently, using the binding nut just above the 
large dial ring for releasing and clamping. If only a small motion of 
the date dial is necessary, it is generally preferable to set it by the 
epee crank. The year index should be set to indicate the kind 
of year. 
408. In the usual operation of the machine a ratchet prevents the 
operating crank from being turned backward, but this ratchet may 
be released when desired by pressing on a button in the side of the 
machine just above the crank. After the face of the machine has 
been thus set to register the beginning of the predictions the three 
main vertical shafts should be clamped to prevent them from turning. 
409. To set the height amplitudes.—All the constituent cranks on the 
left or height side of the machine are first turned, by means of the 
releasable gears on the main vertical shafts, to a vertical position, the 
cranks of the upper range of constituents pointing downward and 
those in the lower range upward, in which position all angles will read 
180°. For the long-period constituents the cranks can be more 
quickly brought to the vertical position by drawing out small knobs 
on the time side of the machine, thus disconnecting the gearing. 
The cranks are then turned by hand to the desired position and the 
knobs pushed back into place. The amplitudes may now be set 
according to the scales attached to the sides of the machine. The 
crank pin is unclamped by a small milled head wrench and is then 
moved along its groove until the index at the scale registers the 
amplitude setting given in Form 445, when it is clamped in this posi- 
tion. If no amplitude is given for any constituent, the corresponding 
crank must be set at zero. 
410. To set time amplitudes —The process is similar to that for the 
height amplitudes, the cranks on the time side of the machine being 
first turned to a vertical position with all angles reading 90°. The 
cranks are to be set with the same amplitudes as were used for the 
height side, the modified scales automatically taking account of the 
true differences in the amplitudes. For the constituents Sa and Ssa 
the amplitudes are set on the height side only. 
