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Thank you Robin and Stan.  Shortly after posting, I started putting a few lines on paper and came up with the roughly the same idea.  I wanted to use it, because I want to make my own calculation and plotting sheet, which can be much simpler if you’re in a static situation compared to a moving one.  I notice most people use an azimuthal projection based on their DR position, but I want to use the intercept method in conjunction with AP3270, so I need to stick with whole numbers of degrees, lat and long, and orthogonality, so I thought I’d better stick with Mercator.  That means I can also trace in a rough topographical background as well.  DaveP