[c172guy]

I wonder about distances from a chart. Only the latitude is accurate and if it''s a mercador projection a straight line is about 12% longer than a great circle route.
This came up because I didn''t have the correct chart handy and wanted to estimate time in route.
If I am actually on the boat I just enter the destination into the gps and it gives all the navigation data. But what if it dies??? I like to be able to dead reckon. I figure the more stuff I know the better.