from the downtrace by a standard amount, say 5°, thus producing two independent 

 traces which can be distinguished at all times, and which nevertheless still can be 

 superimposed for comparsion by any number of simple techniques. 



A further disadvantage of the superimposition is that often times the entire top 

 portion of the trace is destroyed by the pen arm after the Bathythermograph has 

 surfaced and skips along the waves. The jarring and jolting of the pen arm causes 

 the destruction. A pen lifting attachment which removes the pen from the trace in 

 the last 50 feet of travel has been described previously in the literature. This is an 

 advisable procedure in that it will preserve the downtrace of the pattern. 



5.6.4. Bellows Failure 



The 900 foot Bathythermographs have been demonstrating a high percentage 

 of bellows failures through fatigue. Failures have been occurring after one hundred 

 to two hundred lowerings ; there is even skepticism as to the accuracy of the depth 

 sensing elements even before complete failure. One example was cited where a cruise 

 ■ivhich was carrying eight 900 foot Bathythermographs failed to bring back one op- 

 erable instrument, all having failed because of bellows fatigue. The remedy seems to 

 be in the type of bellows used and the mechanism for strengthening and guiding the 

 bellows. Corrective measures are being taken by the Bureau of Ships. 



5.6.5. Loose Parts 



A great many Bathythermograph traces are rendered invalid because of loose 

 parts such as the pen arm, producing hysteresis and distortion. The best remedy for 

 this is more frequent checking of the Bathythermographs during operation by 

 qualified personnel. 



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