Title: Navigation without numbers
Description: From the comments that I read it is a description of a method to find your position at sea with the help of a sextant measurung 
two altitudes.BUT INSTEAD OF THE complex calculations that normally are used ;this method works on a graphical way.So with a compaass and a ruler!
Quite interesting for whom is interested in the subject ,even in this are of G.P.S.!
Subjects: Navigation, sextant, double altitude
Time periods: 1951 about