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Ken,

I have never used one of the W&P slide rules but it did look like
something a beginner might find useful when I read the internet
description. Not something NavListers would need.

Greg

On Jun 28, 4:16�pm, Ken Gebhart  wrote:
> Greg,
>
> I don't think this is it. �The W&P "slide rule" is not a slide rule �
> at all. �It has no logarithmic scales on it. �You can only add or �
> subtract hour angles on it. Not very useful. �I post this so that no �
> one will waste their money buying one on eBay.
>
> Ken Gebhart
> On Jun 27, 2009, at 8:38 PM, Greg Rudzinski wrote:
>
>
>
> > Andrew,
>
> > I believe the time diagram refered to is the Weems & Plath celestial
> > slide rule. Google search this item for a description then look one on
> > eBay.
>
> > Greg
>
> > On Jun 27, 5:27 pm, Andrew Corl  wrote:
> >> I am interested in this diagram, �where can I find it?
>
> >> Andrew
>
> >> ________________________________
> >> From: chempro 
> >> To: NavList 
> >> Sent: Saturday, June 27, 2009 11:00:31 AM
> >> Subject: [NavList 8849] Re: Formulas to Compute LHA
>
> >> Why dont you learn to use a TIME DIAGRAM? It simplfies ALL of the
> >> concepts.It can universally used for all reduction methods from �
> >> Ageton
> >> to NASR. Chempro-Dr Will
>
> >> On Jun 24, 8:07 am, Gary LaPook  wrote:
>
> >>> To see that you can use hour angle and LHA equally well, you just �
> >>> have
> >>> to look at H.O. 249. Look at the LHA columns at each edge of the �
> >>> page
> >>> and you will see that you get the same Hc for two values of LHA. �
> >>> Look at
> >>> LHA 10 and LHA 350 on this example page:
>
> >>>http://www.fer3.com/arc/img/106576.2007-page%20152.pdf
>
> >>> LHA 10 is the same as hour angle 10 west., LHA 350 is the same as �
> >>> hour
> >>> angle 10 east.
>
> >>> This relationship is not so evident if you just look at H.O 229 �
> >>> due to
> >>> the arrangement of the tables.
> >>> gl
>
> >>> Gary LaPook wrote:
> >>>> Remember, LHA is in the range of 0� to 360� and is always �
> >>>> measured to
> >>>> the west from the assumed longitude (ALon). It is the angle �
> >>>> measured
> >>>> westward from the meridian of the ALon to the meridian �
> >>>> containing the
> >>>> body's grographic position (GP). There is no such thing as �
> >>>> easterly LHA.
>
> >>>> In the past, various computations methods and tables (e.g H.O. �
> >>>> 214) used
> >>>> "hour angle," (abbreviated "H.A." or "H" or "t"), which is the �
> >>>> angle
> >>>> measured between the meridian of the ALon and the meridian �
> >>>> containing
> >>>> the body's GP measured the shortest way, either west or east. �
> >>>> Using this
> >>>> notation, hour angle ends up in the range of 0� to 180� only and is
> >>>> denoted "east" or "west." Because of the the way the trig �
> >>>> formulas work,
> >>>> using either method computes the same Hc and the same "azimuth �
> >>>> angle"
> >>>> ("Az" or "Z"). The only thing affected by choice of notation is the
> >>>> method used for the final determination of Zn,(azimuth used for �
> >>>> plotting
> >>>> the LOP.)
>
> >>>> The original Bygrave used hour angle, not LHA, and the scales were
> >>>> marked from 0� to 90� and then back the other way, 90� to 180�. My
> >>>> implementation of the Bygrave eliminated the second set of �
> >>>> markings on
> >>>> the scale, 90�-180�, to eliminate clutter so I added an extra �
> >>>> step to
> >>>> bring hour angle into the range of 0� to 90� only and provided the
> >>>> necessary rules for the final computation of Zn. This is what is
> >>>> happening on the top of the form I provided. If LHA is less than �
> >>>> 90�, H
> >>>> = LHA; if LHA is greater than 90� but less than 180�, H = 180� - �
> >>>> LHA; if
> >>>> LHA is greater than 180� but less than 270� then H = LHA - 180�; �
> >>>> and if
> >>>> LHA is greater than 270� but less than 360�, H = 360 �- LHA.
> >>>> Conceptually, this is the smallest angle measured from either �
> >>>> the upper
> >>>> branch or from the lower branch of the observer's meridian to the
> >>>> meridian containing the body's GP.
>
> >>>> See the revised form at:
>
> >>>>http://www.fer3.com/arc/img/108719.revised%20form%206-18-09.pdf
>
> >>>> The formulas for calculating LHA are:
>
> >>>> If your AP is in west longitude: LHA = GHA - ALon. (If �
> >>>> necessary, add
> >>>> 360 �to GHA prior to subtracting ALon.)
>
> >>>> If your AP is in east longitude: LHA = GHA + ALan. (if LHA then �
> >>>> exceeds
> >>>> 360�, subtract 360� from the result.)
>
> >>>> Using the first formula for your first two examples, GHA (55� + �
> >>>> 360�) -
> >>>> 77� = LHA = 338�.
>
> >>>> GHA 95� - 77� = LHA = 18�
>
> >>>> The third example you bring up makes no sense since GHA is never
> >>>> measured to the east, it is always measured west from Greenwich.
>
> >>>> gl
>
> >>>> Andrew Corl wrote:
>
> >>>>> All,
>
> >>>>> I need some help. �I am attempting to work the problem in Ocean
> >>>>> Navigator using the Lapook-Bygrave Slide Rule. �I am uncertain �
> >>>>> how to
> >>>>> compute the Local Hour Angle (LHA).
>
> >>>>> In the following cases I am assuming my longitude to be 77 degrees
> >>>>> west of Greenwich.
>
> >>>>> 1. The GHA of the Sun is 55 degrees west of Greenwich
> >>>>> 2. The GHA of the Sun is 95 degrees west of Greenwich
>
> >>>>> In the following cases I am assuming my longitude to be 120 �
> >>>>> degrees
> >>>>> west of Greenwich
>
> >>>>> 1. The GHA of the sun is 170 degrees east of Greenwich.
>
> >>>>> Also what is the formula if my position is east of Greenwich �
> >>>>> and the
> >>>>> sun has a GHA of more than 180 degrees?
>
> >>>>> Thanks
> >>>>> Andrew- Hide quoted text -
>
> >>> - Show quoted text -
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