RATING TABLE— ROBERTS RADIO CURRENT METER MODEL II 



Note. — Derived from calibration tests. 



are less than 4 seconds, the averaging of a scries 

 as described above sliould be so performed as to 

 result in values of timc-per-contact interval 

 correct to 0.01 second. For values between 4 

 and 12 seconds, the time-per-contact interval 

 should be determined to the nearest 0.1 second. 

 For greater intervals, whole seconds will suffice. 

 The foregoing presupposes final results correct 

 to 0.1-knot current velocity. 



If the chronograph has a speed control, it 

 is convenient to condense the record by op- 

 erating at slow speed where the time intervals 

 are long and do not require close scaling. 



3. Direction Indications. — These are deter- 

 mined by use of a transparent scaling device, 

 shown in figure 9-8, having converging lines 

 representing 10-degree increments from 0° at 

 the left to 360° at the right. Being sure that 

 the tape is laid before the observer with 

 chronological order advancing from left to 

 right, this scale is laid over the tape so that 

 the outside (0° to 360°) lines coincide with the 

 beginning points of two successive V-marks, 

 having a D-mark between them. The begin- 



ning point of the D-mark is read from the scale 

 to the nearest 5° or 10°. This is the magnetic 

 direction of current flow. 



Obviously, depending on the mechanical 

 construction of the chronograph and the nature 

 of its recorded marks, these instructions may 

 require modification. For instance, if the 

 chronograph record is more conveniently used 

 with chronological order reversed (advancing 

 from right to left) the direction indicator scale 

 can be marked to show 0° at the right and 360° 

 at the left. 



General uniformity of spacing of marks wiU 

 prevail. However, irregularities may result 

 from swirl conditions at the current station, 

 or choppy waters combined with weak current. 

 Here mean values of several readings should be 

 employed. 



Good practice includes a plot of each di- 

 rection and velocity against time, as soon as 

 recorded, on any convenient coordinate paper. 

 The resulting curves will, in most cases, reveal 

 promptly any fault of operation or scaling 

 which might require immediate correction. 



H. O. 607 



350676 O — 56 



101 



