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## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Scientific calculators - statistics mode
From: Bela Kovacs
Date: 2021 Nov 30, 07:10 -0800

Last year I mentioned I use Sharp calculator for navigation calculations (because older models can store formulas):

http://fer3.com/arc/m2.aspx/Casio-fx300ES-Plus-2nd-Edition-Kovacs-nov-2020-g49133

I read the manual and I saw there's a statistics mode.
I've some ideas, please correct me if I am wrong:

Linear regression with 2 points: (x1, y1) and (x2, y2) is linear interpolation.
So I can interpolate UT and GHA from almanac (entering values directly using sexagesimal).

Quadratic regression is determining the equation of a parabola.
y = a + b*x + c*x^2
The derivative is:
y' = 2*c*x + b

Time of maximum altitude means y' = 0:
x = -0.5 * b / c
(convert result to sexagesimal)

I checked it with some sights (15 height values, 30 minutes interval). Error was only 15 second.
// Correction for vessel motion (in seconds): t = (48 / PI) * (Sn - d)(tan(Lat) - tan(Dec))

I tried the paper folding trick. Maybe it is a good estimate where to start folding.

Thank you,
Bela

PS: I found this later:
http://fer3.com/arc/m2.aspx/LAN-curve-parabola-FrankReed-nov-2019-g46215

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