NavList:

For those that are game for trying the time sight reduction by slide rule there are a few ways to gain some accuracy. A means to magnify the slide rule scale goes without saying.

1. Use a four place SinHo look-up from the Bowditch trig table.
2. Use the Bowditch trig table for the final ArcCos look-up to get LHA (t) meridian angle.
3. Slide rule alignment on the two multiplications can be improved if a whole latitude is used.

This will result in two table look-ups, two slide rule multiplication moves, one slide rule division move, and one conventional sum.

Greg Rudzinski

[NavList] Re: Longitude by Time Sight Using a Slide Rule
From: Greg Rudzinski
Date: 14 Dec 2012 10:18

K&E slide rule accuracy seems very good for LHA(t) meridian angles greater than 50*. There is no need for small meridian angle calculations when the ex-meridian method would be used. See attachment for this mornings time sight by slide rule. The plot exactly matched an azimuth and intercept by computer reduction.

Greg Rudzinski

[NavList] Longitude by Time Sight Using a Slide Rule
From: Greg Rudzinski
Date: 14 Dec 2012 09:03

The K&E 10" has been dusted off to perform some time sights using the formula:

LHA(t)=ArcCos[ (SinHo ~ SindSinL) / (CosdCosL)

~ add if contrary name
~ subtract if same name
t = meridian angle
Ho = true altitude
d = declination
L = Latitude

This seems to be accurate enough. If Paul Hirose is watching then maybe he can do a slide rule accuracy analysis for the time sight using the 10".

Greg Rudzinski

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