Hmm that makes me wonder on the method for determining speed. you can count how many second it takes for the target to cross your 0 or 180 marks. Was that usual practice or did they plotted speed?
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"Listen, 'sir', it's real simple. Add the number of times we dive to the number of times we surface. Divide that number by two. If the result doesn't come out even, don't open the hatch"
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