REDUCTION OF CURRENT RECORDS 49 
Obtain the velocities corresponding to the number of contacts from the rating table and 
enter in the fifth column of the form. The times given in the first column should refer 
to the middle of each observational period, which will be an exact hour or an exact 
fifth of an hour. For another method of interpreting the graphic record without the 
rating table see paragraph 63. Table 2 is also applicable if the number of revolutions 
of the meter wheel per minute is first obtained by multiplying the number of contacts 
by the denominator of the contact ratio and then dividing by the number of minutes 
in the period covered by the count. 
127. When the Ekman current meter is used, the number of turns of the meter 
screw in a specified interval of time is determined by the difference between dial read- 
ings taken at the beginning and end of the time interval. The observer is expected to 
record in a suitable note book these dial readings with the times of the observations. 
The difference between successive dial readings obtained by subtracting each reading 
from the one that precedes it (dial readings decrease with operation of meter) may then 
be entered in Form 270 together with the period covered by the observation. The time 
of the observation should be entered in the first column of the form. As each observa- 
tion usually covers a number of minutes, that given in the record may be either the 
middle of the period or should indicate both beginning and end of the observation. 
Next, the velocity of the current for each observation is obtained by a suitable formula 
or rating table (par. 80). Table 4 has been prepared for use with meter No. 110. 
This rating table provides directly for a 1-minute observational interval, but when the 
period of observations covers a number of minutes, as is generally the case with the 
Ekman meter, the number of revolutions of the meter screw should be divided by the 
number of minutes covered by the observation to obtain the average for 1 minute which 
is used in entering the table. 
128. It will be noted (par. 65) that the limit of the accumulated count of the 
Ekman meter is 4,000 revolutions, after which the instrument begins to repeat. In 
obtaining differences between successive dial readings, this fact must be kept in mind. 
Usually there will be little danger of misinterpreting the record on this account pro- 
Tasie 3.—Rating table for Price current meter for graphs from automatic recording device 
Velocity Velocity Velocity Velocity 
Meares FFF SSS contacts _ FSF Contacts a Se peontacts SS 
In - urin: - a a 
minute | Reord-| Record: |] “rinmte | Repord-) Reoord- |] “riintze | Reoord-| Reoord- |] “Trintte | Record. | Record- 
period ratio ratio period ratio ratio period ratio ratio period! ratio ratio 
1:10 1:50 1:10 1:50 1:10 1:50 1:10 1:50 
Knots Knots Knots Knots Knots Knots Knots Knots 
NF re 0. 04 Qi) Wo es 0. 31 I, GW) Bilsa—e= 0. 58 2.8 || 46--__- 0. 85 4.2 
ee ee . 06 SMe db . 33 1 || ee cease . 60 , Q Wee = . 87 4.3 
Sys aoe . 08 o@ |, WB == . 34 I, @ || @Booa-5 . 62 3,0) |) Zh = . 89 4.4 
fee . 09 omail|) ue) ee . 36 ik. ||| Hs . 63 3.1 || 49_-_--- . 90 4.5 
a seese -11 66) |i) AQsos=- - 38 IES |) Sys oas= . 65 3.2 || 50--__- . 92 4.6 
Giza ss 13 OR ||e oie . 40 iL Or Sse - = . 67 88} ii) Sile_ = . 94 4.7 
(ES 15 Seles (B22 . 42 20) ||) Besos . 69 Ss CEI GY eae . 96 4.8 
Seen . 16 sulta| | 232 ao . 44 72 Wil ete ee . 70 3: 0) ||) Ode s2—— . 98 4.8 
OF Se. 18 08 ||pot nee . 45 2; 7M CQess= = . (2 a © ||| Gytoea2e 1. 00 4.9 
lO . 20 5 Oil 2issse= AT 2.3 || 40__-_-- 74 Sell OD see 1. 01 5. 0 
ile . 22 Qi) Ags a2 2= . 49 2.4 || 41_-___ . 76 3.8 || 56_-____ 1. 03 5. 1 
QE 2 . 24 Wok Wy) Bevsese = . dl 25) |i) Cn . 78 &, 8 lll G/2- ese 1. 05 5. 2 
iS eee . 26 2 i) ASa— = = . 52 2» @ ||| 4-2 o— . 80 ay 9) il) Ges ee 1. 07 5. 3 
ee en 27: LES i209) . 54 2.7 || 44____- . 81 AS 05 || to92ea2= 1. 09 5. 4 
oR Se! . 29 GE Wei) . 56 PA i Gus = . 83 4.1 || 60___--- 1. 11 5.5 
