WW2 Era Naval Harmonic Analysis Form – Sonar Plotting Sheet

I cant find another comparison for this sheet so will endeavour to tell you what I can, aside from the heading of harmonic analysis form – plotting sheet it is double sided with the 24 hour clock times down both sides, a grid to the middle with equally spaced plotting dots. Both sides are the same but one is laid out larger than the other, I thought it might have something to do with Sonar plotting perhaps for a submarine. It came with a large selection of WW2 Naval maps and paperwork, there are 9 in all and are in very good condition, they each measure 17.5 x 17.5 inches and will be sent rolled.