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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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