...and so what might 2M19 according to the 'American practical navigator' in an alternate universe?

https://books.google.co.uk/books?id=CAWtAAAAMAAJ&pg=PA258&lpg=PA258&dq=what+does+2M19+mean&source=bl&ots=mdUWoy7j44&sig=p6SP1q1dNUBa6d6aALGihZQPJw8&hl=en&sa=X&ved=0ahUKEwjVwuyY5c7NAhUJJsAKHZ6RByAQ6AEINzAG#v=onepage&q=what%20does%202M19%20mean&f=false

a chronometer....what else? the abaft...and the neap tide....and you wonder why you had to learn how to do logarithms at school?