142 U. S. COAST AND GEODETIC SURVEY 
415. In setting up the machine for successive stations there is a 
mechanical advantage in making the necessary gear changes before 
setting the new amplitudes if the gear changes are in the order of 
2:1, 3:2, 1:1, and after setting the amplitudes if the gear changes 
are in the reverse order. This precaution will lessen the chances of 
jamming the curve pen carriage and throwing the height chain off its 
pulleys when setting the amplitudes. 
416. Inserting paper roll——To place the paper on the machine, re- 
move the mandril that is mounted within the dial case near the upper 
right-hand corner and slip the roll of paper over the mandril, the 
roll being so placed that the winding is clockwise when viewed from 
above and when on the machine the paper unwinds from the outer 
side of the roll. In placing the roll on the mandril care should be 
taken to see that the small projection on the base of the latter enters 
the cavity in the wooden core, so that the roll will fit flat against the 
base. After the mandril with the roll of paper has been returned to 
the machine and secured in place, the end of the paper is passed around 
a roller to the face of the machine, across the face, and over the feed 
roller at the left of the machine. The end is then inserted into the 
slit in the receiving roller, which is given a few turns to take up the 
slack paper and make it secure. Before passing the paper over the 
feeding roller and on the receiving roller these rollers should be released 
to permit them to turn independently, the release being effected by 
turning the small milled head on a ratchet stud gear near the base of 
the feeding roller and by lifting off from the top of the receiving roller 
the small knob holding the connecting chain. After the paper has 
been secured to the receiving roller these connections should be 
restored. 
A417. Curve pen adjustment.—With the machine in its mean sea-level 
position, the curve pen must be adjusted to bring the pen point on 
the mean sea-level line as drawn by the base-line pen. This adjust- 
ment may be effected by releasing the pen carriage from the oper- 
ating chain and moving it to the desired position, where it is clamped 
in place by the binding screw. 
418. Verification of machine settings.—Each step in the adjustment 
and setting of the machine should be carefully checked before pro- 
ceeding with the next step. After the setting of the machine for any 
station has been completed an excellent check on the work is afforded, 
if the predictions for the same station for the preceding year are 
available, by turning the machine backward several days and then 
comparing the predicted tides with those previously obtained. 
419. Predicting —The datum and curve fountain pens are filled and 
put in place, the electric cut-out switch under the base of the machine 
closed, and the ratchet of the operating crank set to prevent the 
machine from being turned backward. If the predicted height of the 
tide for any given time is desired, the machine may be turned forward 
until the required time is registered on the time dials and the cor- 
responding height read off of the height dial. 
420. If the predicted high and low waters for the year are desired, 
the operating crank is turned forward until the machine is auto- 
matically stopped by the brake at a high or low water. To avoid the 
strain on the machine due to sudden stops, the operator should watch 
the small index on the time chain, and as this approaches the fixed 
index in the center of the opening on the face of the machine, turn the 
