Figure M-2Ji. Annotating the GEK record. 



cruise name and number, the GEK instrument 

 number, the GEK serial number or consecutive 

 number for eacli fix, commencing with the nu- 

 meral 1 for the first fix of each cruise, the clay, 

 month, year, and the hour and minute (G.M.T.) 

 for the beginning of the current fix; i.e., the 

 start of the 4-minute run on the initial base 

 course. 



Stei^ 2. Record, in the Vertical Magnetic In- 

 tensity column the F dial setting (Stand I) of 

 the GEK at the time of the current fix and the 

 standard isodynamic value (Local II) for the 

 position of the current fix taken from H.O. 

 Chart 1702, the vertical intensity of the Earth's 

 Magnetic Force. Record to the nearest 0.005 

 oersted. On the strip chart, enter the wave- 

 signal suppression, the FILTER RESIST- 

 ANCE dial (H) setting, e.g. C=0. 



Step 3. Record the Initial Base-Course Di- 

 rection III in degrees true and Signal- IV in 

 centimeters per second. The signal is obtained 

 from the chart during the 4 minutes prior to 

 the first course change. The instrvunent zero 

 is the centerline of the strip chart and the range 

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

 left respectively of this line. 



Step 4. Record the First Fix-Course Direc- 

 tion V in degrees true and the Signal VI as in 

 step 2 above, and annotate the recorder chart 

 with the course change as follows: 



Change 1—1970 



22gF^0358Z (GEK serial No. 1 fig. M-23). 



If the wave signal suppression is changed 

 during a run, annotate the strip chart as 

 follows : 



CO 

 C2 



(G.M.T.) . 



Step 5. Record the Second Fix-Course Di- 

 rection VII and Signal VIII as above. 



Step 6. Record the Resumed Base-Course Di- 

 rection XI and Signal X as above. 



Step 7. Record depth of water in meters or 

 fathoms using Sonic depth at the time of the 

 Ijeginning of fix, the ship's position at the time 

 of the beginning of the fix, and the sliip's aver- 

 age speed in knots during the fix. 



During a GEK run, the operator should be 

 alert for spurious records caused by cable 

 failures. 



NOTE: Use one line for each GEK serial 

 No., and use remarks section to enter signifi- 

 cant information concerning depth, wind direc- 

 tion, and sea state. 



M-33 Reading the GEK Strip Chart.— In 



reading the voltage signals on the strip chart, 

 some variability of results will be ine\atable 

 from person to person. Tlie principal sources of 

 this variability arise in makmg estimates of the 

 average voltage due to the mean water current 

 through the confusion of turbulence and wave 

 signals and in making estimates of each turn 

 signal. Better results are obtained in determin- 

 ing the average voltage if clone entirely by eye 

 without the use of pencil marks or a ruler. Esti- 

 mation of the beginning and end of a turn sig- 

 nal can be aided by measuring the interval of 

 time during execution of a turn. Inasmuch as the 

 electrodes are towed at a considerable distance 

 behind the ship, there is a lag in the electrode's 

 turn signal. Thus the electrodes do not steady 

 on the new course for a minute or so after the 

 ship has steadied and similarly do not com- 

 mence their turn when the ship commences turn- 

 ing. The tuni signal lasts as long as the ship's 

 turning time and is received approximately 

 L/C3 minutes after the ship has commenced 

 turning. L is the length in meters of the cable 

 towed astern, and C3 is the ship's sjjeed in meters 

 per second. Anticipating and marking the begin- 

 ning and ending of the tuni signals as they 

 occur will improve the consistency of interpreta- 

 tion of the data, both at sea and in later study 

 of the records. It is well to be extravagant in de- 

 lineating the turn signals, for if the voltage 

 shift on the two courses is large, both the elec- 

 trodes and the capacitors in the wave-signal 

 suppressor (filter resistance) must liave time to 

 come to equilibrium. 



M-23 



