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    GPS AntiSpoof and SD contraction
    From: Modris Fersters
    Date: 2023 Mar 4, 06:20 -0800

    Frank’s GPS AntiSpoof app is an excelent way to check a sextant. I started to think: does the app take into account SD contraction when low altitudes are taken? The errors may be quite large if this is ignored, esspecially when AH is used (errors of SD values would be doubled). For example if apparent altitude is 5°, error using artifical horizon would be about 0,8’. If altitude is 6°, then doubled SD error would be 0,6’. These are easily measurable values for good metal sextant.

    Of course, SD contraction is typically ignored in “standart celestial navigation” for altitude sights (it is actual only for lunars), but I am still curious, is this phenomen included in app?

    I suspect that GPS Anti Spoof takes SD compresion into account but I would like to ask Frank about this to be 100% sure.

    Modris Fersters

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