And that is realistic. TDC operator, sonar operator and radar operator could all input a range in yards into the TDC directly. What is not accurate about OTC is that it has a perfect record of all characteristics of every ship on the ocean, where the real TDC had less than half, plus much of the info it had was wrong.
Therefore the necessity, according to Lockwood, of taking a single ping range at somewhere in the neighborhood of 3000 yards so the periscope operator could manually enter the masthead height that yielded the same number as the sonar range. Thus calibrated, the stadimeter would be accurate for that ship only for the rest of the encounter.
Now here's where the logic comes in. If the recognition manual contained accurate information on every ship on the ocean, Lockwood would not say it was a necessity to ping at 3,000 yards to calibrate the masthead height so the stadimeter was worth more than the backgammon table in the crew's mess. Therefore, it was expected that most information on the sub was bad enough to make it necessary to risk the ping.
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