MANUAL OF TIDE OBSERVATIONS 59 



194. Cleaning stylus screw. — For the efficient functioning of the 

 gage it is important that the stylus screw be cleaned at frequent 

 intervals. This should be done in the same manner as with the pencil 

 screw of the standard gage. (See pars. 129-131.) 



195. Cleaning float pipe. — If the gage is to be operated for a con- 

 siderable period of time the float pipe should be cleaned occasionally 

 to prevent the opening in the conical inlet coupling becoming clogged, 

 It should be cleaned by removing the float from the pipe, inserting 

 the cleaning tool to which a line has been attached, and raising and 

 lowering it several times in the pipe. (See pars. 132-134.) 



196. Comparative note. — Each day the tide gage is visited, a com- 

 parative note giving the date, the correct time, and staff reading 

 should be entered on the marigram (fig. 22). The stylus is to be 

 adjusted when necessary to agree with the correct time and staff 

 reading. As unbiased staff readings are necessary for the proper 

 reference of the various tide planes to bench marks, care must be 

 taken by the observer to avoid being influenced by a previous setting 

 of the stylus on the cross-section paper when taking a new staff 

 reading. However, when an unusual rough state of the water renders 

 a staff reading somewhat unreliable, a previous setting of the stylus 

 under more favorable conditions should be retained without change. 



197. To indicate on the tide curve the exact point to which the 

 comparative note refers, first rock the stylus holder (35, fig. 13) slightly 

 to make a short line parallel to the edge of the paper. Next place 

 the hand lightly on the float drum (17, fig. 12) and raise the float a 

 little way out of the water and then lower it, making a short vertical 

 line on the marigram. The point indicated by the intersection of 

 these lines is then connected with the comparative note by a light 

 line. 



FIELD REDUCTIONS 



198. Preliminary computations of tidal data to obtain tide reducers 

 for soundings are often carried on in the field.. The processes are 

 covered in the following chapter on Tabulation and Reduction, but 

 for field purposes, parts of the instructions not directly applicable to 

 the work in hand may be omitted. Unless there is special need to 

 expedite the reductions in the field the planes of reference for the 

 reduction of soundings will be furnished by the office upon the receipt 

 of the original tide and leveling record. 



TABULATION AND REDUCTION 



PRELIMINARY WORK 



199. The original tide records to be tabulated will vary in form 

 according to the kind of tide gage used in taking the observations. 

 The records generally consist of tide rolls from the standard automatic 

 tide gage or tide sheets from the portable automatic tide gage. The 

 following general instructions are applicable to the several forms used 

 for the tabulations and reductions. The work is to be done neatly 

 and in ink. Interpolated or inferred values are to be indicated by the 

 use of brackets. The heading on each sheet will in general be filled 

 out as completely as possible in order that it may be fully identified, 

 but when a tabulation covers several sheets a repetition of the latitude 



