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    Re: Units in Navigation
    From: Brian Walton
    Date: 2020 Sep 24, 21:32 -0700

    Hello,

    People started to pay me to fly aircraft in the late 1950s. Nato and western civil  international aviation used knots and feet, but Russia and China didn’t. You set your altimeter to “ queen-nan-how” in whatever the subscale read, mbs, or “/hg.

    Maps were drawn to whatever scale the country you were in used. Often kms and metres, perhaps “ fifty thousand” or inches per statute mile. A nautical mile is about 2 km. That was close enough.

    It was the era of “under the radar”, no calculators. To make mental arithmetic easier, you flew at speeds in miles per minute. 240/360/420 kts = 4/6/7 miles per minute. If you had time to plan, you used a self-made Perspex strip ruler notched at every, say, 7 miles. That way, you could run a grease pencil down the edge, and have your track marked in minutes on the map.

    Then they went metric and decimalised in lots of countries. Try CN in rads and kms, Then along came cheap scientific calculators.

    I stilll fly old aircraft calibrated in mph, feet and “/hg, but just across the water they use decimal  kmph and metres, to make it easier, they say.

    Guess what, I still have a sexagisimal watch running on hours, minutes and seconds.

    Brian Walton

       
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