(I used to work on underwater sonar)
Hey so did I, at Portland.
which is why i was wondering why didn't they set it to 2
For a beginner it is difficult to know that some things are just a guess in the right order of magnitude and that it doesn't matter much the exact value. For example the base resistor in a transistor could be anything between 1K and 10K with out it mattering much. I suspect they tried 5mS and that worked so they stuck to it.