134 U. Sf COAST AND GEODETIC SURVEY 
fore the scale of the chain motion is 1 inch to the unit, and one com- 
plete rotation of the summation wheel represents a change of 12 units 
of amplitude. 
383. The zero position of the height summation wheel is indicated by 
the conjunction of an index line (40, fig. 25) on the arm attached to 
the wheel and an index line (1, fig. 25) on a bracket attached to the 
framework of the machine just below the summation wheel, the 
wheel itself being approximately one-half filled with the summation 
chain. The length of the chain is adjusted so that the summation 
wheel will be in its zero position when all the sliding frames on the 
height side of machine are in their zero positions. It will be noted 
that the conjunction of the index lines will not alone determine the 
zero position of the wheel, since such conjunctions will occur at each 
turn of the wheel, while there is only one zero position, which is that 
taken when the constituent frames are set at zero. 
384. The zero position of the time summation wheel is indicated by 
the conjunction of an index point (11, fig. 23) attached to the time 
summation chain and a fixed index (12, fig. 23) in the middle of the 
horizontal opening near the bottom of the dial case, and the length of 
the time summation chain is so adjusted that this conjunction will 
occur when all sliding frames on the time side of machine are in their 
zero positions. : 
385. Predicted heights of the tide—When the machine is in operation, 
the sum of all the cosine terms of formula (458) included in the settings 
for a station will be transmitted through the height summation wheel 
to the face of the machine and there indicated in two ways—first by 
a pointer moving over a circular height scale (8, fig. 23) and second 
by the ordinates of a tide curve that is automatically traced on a 
roll of paper (16, fig. 23). The motion of the height summation wheel 
is transmitted by a gear ratio of 30:100 to a horizontal shaft which 
is located just back of the dial case. One complete rotation of this 
shaft represents 40 units in the height of the tide. From this shaft 
the motion is carried by two separate systems of gearing to the height 
pointer on the face of the machine and to the pen that traces the 
tide curve. 
386. Height scale-—The height pointer is geared to make one com- 
plete revolution for a change of 40 units in the height of the tide. A 
height scale, with its circumference divided into 40 equal parts and 
each of these unit parts subdivided into tenths, provides for the direct 
registering of the sum of the cosine terms of formula (458) as com- 
municated through the summation wheel. This scale has its zero 
graduation at the top and is graduated positively to the right and 
negatively to the left. The height pointer can easily be adjusted to 
any position by means of a small milled nut (10, fig. 23) at the end of 
its shaft. Ifit should be desired to refer the predicted heights to mean 
sea level, this pointer must be adjusted to read zero at the same time 
that the summation wheel is in its zero position; but if it is desired 
to refer to some other datum, the pointer will be adjusted according 
to the elevation of mean sea level above this datum. For the value 
of h in formula (458) the pointer will be adjusted to a reading corre- 
sponding to the adopted value of H, at the time the summation 
wheel is in its zero position, then this value of H, will be automatically 
included with the sum of the cosine terms of that formula. As the 
