44 U. S. COAST AND GEODETIC SURVEY 



If desired the times may be expressed according to the 24-hour 

 system in which the hours are numbered consecutively throughout 

 the entire day thus avoiding the necessity of using the designations 

 "a. m." and "p. m." If the usual 12-hour system is used care must be 

 taken to indicate the forenoon and afternoon hours by their custom- 

 ary designations. 



123. At the beginning of the record on a tide roll the correct time 

 and the gage time should be in agreement. In subsequent notes the 

 difference between the correct time and the gage time will indicate 

 how much the time clock of the gage has gained or lost since the 

 previous note was entered. After each entry has been made the 

 time clock should be set to agree with the correct time. The minute 

 hand of the clock, however, must not be turned backward when be- 

 tween 10 minutes before and 5 minutes after the hour. (See pars. 

 22-23 for setting and regulating clock.) 



124. Reading tide staff. — In taking the tide staff reading, both the 

 highest and lowest points reached by the waves are to be recorded, 

 the two readings being separated by a dash or in some other distinc- 

 tive manner. If a glass tube is used the height of the water in the 

 tube should also be recorded. 



125. The observer will note that the tide staff is graduated in tenths 

 of feet and not inches. The heights in general are to be read to 

 the nearest tenth or half -tenth of a foot, the half -tenth being recorded 

 as 5 in the second decimal place. When the staff is equipped with 

 a glass tube (par. 7) the staff reading corresponding to the water 

 surface inside the tube should be read, but the observer must assure 

 himself that the opening in the bottom of the tube is not clogged, 

 and if there is any wave movement on the outside the water in the 

 tube should show a perceptible oscillation. 



126. While individual staff readings may at times seem rough and 

 inaccurate, the final results, depending upon- an average of a great 

 number of such readings over a considerable period of time, reach a 

 very satisfactory degree of precision provided they are taken in an 

 unbiased manner. It is of great importance, therefore, that the tide 

 observer when taking staff readings should be uninfluenced by any 

 other consideration, and such readings should be entirely independent 

 of any scale on the automatic tide gage. 



127. Adjustment of hour-marking device. — Small variations in 

 the hour-marking device on different instruments preclude detailed 

 instructions applicable to all gages now in use. In all cases, however, 

 care must be taken to avoid any binding between the tripping hook 

 (36, fig. 7) -and the tripping rod (26, fig. 7). In the latest type gage 

 the tripping hook must just clear the rod during the first half of each 

 hour. During the last half of the hour the tripping rod gradually 

 recedes from the hook preparatory to striking the hour. When ad- 

 justments are necessary, they should, therefore, be made with the 

 minute hand in the first half of the hour. 



128. Adjustments may be made at four different points and several 

 trials may be necessary before securing a satisfactory operation of 

 the device. One adjustment consists of changing the position of the 

 recording pencil in its holder, the pencil being secured in place by a 

 binding screw (39, fig. 7). A very slight change in the elevation 

 of the pencil and even a change resulting from the wearing away of 



