9-21 Signal Multiplier.— The SIGNAL 

 MULTIPLIER dial increases or adjusts the 

 size of the input (wave) signal. 



9-22 Electrode Zero Point Control.— Be- 

 fore the initial base course run is begun, the 

 zero point can be adjusted to approximately 

 the instrument zero (centerline) by use of the 

 ELEC. ZERO dial. By slowly turning this 

 dial to the right or left, the pen can be brought 

 to the instrument zero point. Once this setting 

 is made, it should not be changed during the 

 period of the actual current observation. 



In the vicinity of the continental margin of 

 the Gulf Stream, the changing temperature 

 and salinity will shift the zero point at each 

 crossing. Study the zero-point trends, and if 

 necessary adjust the zero point before the 

 GEK run so that it will sliift symmetrically 

 about the instrument zero with each crossing. 



9-23 Maneuvering the Ship for a GEK 

 Observation. — The course the ship is required 

 to steer for a GEK observation is determined 

 by the requisites: (a) That potentials must be 

 measured on at least two headings at right 

 angles if possible and (b) that for each current 

 fix the electrodes must be reversed end for end 

 to determine the zero point (the average of 

 the 2 voltages obtained by making a 180° 

 course change). This is accomplished by 

 executing a current fix as follows: 



1. After the electrodes have become thor- 

 oughly soaked and the pen motion has steadied, 

 remain on base course for 4 minutes. 



2. Change course 90° and run for 4 minutes 

 after the electrodes steady-on the new course. 

 This is the first fix course. 



3. Change course 180°, turning in the direc- 

 tion of the base course, and run for 4 minutes 

 after the electrodes steady-on the new course. 

 This is the second fix course. 



4. Change course 90° and resume the base 

 course. Run for 4 minutes after the electrodes 

 steady-on the base course to obtain the resumed 

 base course data. 



9-24 Recording the GEK Data.— The dat^ 

 obtained by executing the current fix arg 

 recorded on oceanographic log sheet — GEK 1. 

 Instructions for filling in this log sheet are given 

 in chapter 14. When filling in the log sheet, it 

 is well to remember that the instrument zero 

 is the centerline of the strip chart and the range 

 is plus and minus 250 cm. /sec. to the right and 

 lejt, respectively, of this line. 



9-25 Marking the Strip-Chart Record.— 

 The measurements require the continuous 

 attention of a trained observer. In addition to 

 keeping the log sheet, it is necessary to record 



90 



the following information on the recorder strip 

 chart: 



1. The GEK observation serial number. 



2. The day, month, and year. 



3. The Greenwich mean time for tlie begin- 

 ning of the first 4-minute base-course run. 

 Additional information as to depth, wind direc- 

 tion and speed, and sea state is helpful to those 

 interpreting the data. 



4. Electric zero setting. 



5. Filter resistance setting. 



During the current fix, the following informa- 

 tion is recorded on the strip chart as indicated: 

 1. A change of wave signal suppression 



C8 

 C6 



0932Z 



2. A course change 



135° T 

 045° T 



2055Z 



The strip chart moves downward under the 

 pen; hence, the line between the changed values 

 of any quantity indicates the moment of 

 change, and the lower value is the condition 

 existing earlier than the upper value (fig. 9-2). 



Figure 9-"^. Marking the GEK record. 



H. O. 607 



