(55) Great Circle Azimuth

[SlideRule]

An extract from Aim Your Beam Right  … with a programmable calculator, 73 magazine {JUN 1976}, pgs.122-123

"
    The recent arrival of programmable pocket calculators at more affordable prices offers the serious ham a new tool to improve his DX through proper antenna orientation … one of those very interesting new calculators that can be taught to perform in seconds what would otherwise be a rather messy calculation …
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… good use for that HP-55 I had bought …
…
… formula which not only could be programmed with a minimum of key strokes, but also permitted the calculator (not me) to determine the short path with a test and conditional branch. The basic formula is included in case you need to modify the instructions for a different instruction sequence (the algebraic vs. RPN system). For Hewlett-Packard and probably other RPN types, you can go right to the program.
…
HP-55 User Instructions … HP-55 Program Form … "

BEST!
SlideRule

ps: see HP Software Libraries / HP-65/67/97 Software Library / (HP-65) Beam Heading & Distance,