Figure II-2 shows the general design of the marker discussed above. 

 The push-button keyboard controls the time of the gate which in turn 

 controls the number of cycles allowed to enter the magnetic tape. 

 Stability of this system is excellent if, for example, 100 cycle increments 

 are used for the digits through 9. Then by detecting the hundreds 

 place, stable digits can be read which are proportional to the annotation 

 information. 



3. Record Playback 



In order to record and playback both the data and the auxilliary 

 information, a two- channel magnetic tape recorder would be employed. 

 The data channel and auxilliary channel would be designed so that 

 encoding of auxilliary information would automatically interrupt the 

 data channel. When the tape is read, the auxilliary information and the 

 data would be read sequentially as a single channel recording. Figure 

 II- 3 illustrates the record and playback technique. 



4. Reading and Printout 



The number of cycles proportional to the digital representation of 

 auxilliary information would be read by an ungated electronic counter 

 triggered and reset by the time interval between digits. The data channel 

 would be read by a gated electronic counter. Both readings then could 

 be printed out on a compatible printer, punched on a card, or converted 

 to EDP equipment tape. 



5. Calibration 



Each transducer would have a calibration certificate which would 

 accompany the instrument. In addition, a punch card file of calibrations 

 for all transducers would be maintained at the Hydrographic Office. 

 This information would be used to convert the frequency to the desired 

 units of measurement. Methods for checking field calibrations would be 

 established and required at specified intervals. 



C. CONCLUSION 



The requirements mentioned in the introduction to this report are 

 believed to be met by the system described. An important criterion 

 for successful data recording and processing with this system is that 

 a standard format for the auxilliary information be established. This 

 system will provide a nearly continuous record of any geophysical 

 variable that can be converted to a variable audio frequency. The 

 readout in the form of punch cards provides for economical and 



II- 4 



