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    Re: Air Navigation, Local Hour Angle Type X-1 computer
    From: David Pike
    Date: 2016 Feb 17, 14:49 -0800

    Ed Popko you wrote: On a whim, I bought a "COMPUTER, AIR NAVIGATION, LOCAL HOUR ANGLE TYPE X-1" plastic circular sliderule.  A simple device which I assume is used to identify bright nav star azimuth for setting up shots. Similar to what HO 249 provides. But there wasnt any flier or example. The printed steps on the back are terse and obtuse, there must have been some additional instruction on how to set the various wheels.

    Essentially you set the device for the local hour angle of Aires and GCT.  The inner wheel is marked with 23 nav stars and their dec which I assume will align with one of the azimuth scales somehow.

    There is an additional window that indicates the correction of Polaris' true azimuth.

    Can anyone point me to some references, perhaps a previous air navigation manual that might have has a short writeup on it?

    Ed.  You might try looking at http://wisvetsmuseum.pastperfectonline.com/webobject/7B2BF95F-D02B-4A3D-AE8C-058595451400 although it might tell you little more than what’s written on the slide rule.  I was interested in the use of GCT, which presumably means Greenwich Civil Time (not Greenland Central Time!), rather than GMT or UTC.  I don’t recall ever seeing that used before.
    Please could you possibly re-photograph your X – 1 and send at again at around 300kb or above.  The one you sent is too pixelly to read the printing in detail.  Please will you also supply a photo of the rear.
    It’s interesting that it goes up to 36 hours.  Could this be to make navigating across the International Date Line easier?
    I wondered if it was primarily for use with an astro compass for heading checks from an aircraft with an astrodome.  You would only have to set true course, LHA body and latitude. 
    Then move the declination bar upwards until hopefully you identified the body in its correct position it its constelation, or set declination from the Air Almanac. Then wiggle the true course plate until everything lined up and you’ve got your actual heading.
    I can’t see a lot of point in it unless you wish to operate without AP3270/HO249.  You still need the air almanac to get GHA Aries, SHA Body, and declination.  Then it’s only simple arithmetic to get LHA Aries and LHA Body. DaveP


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