NavList:

I started off in 1983 with an RAE Mk IXA and a set of AP3270 (British Version of HO 249) Sight Reduction Tables for Air Navigation. I still have both and look at them with fondness because they conjure up good memories of my introduction to what later became a passion.

That being said, I have a solar powered Texas Instruments scientific calculator for which I paid $25.00 15 years ago. Since that time, I have used the trignometric formulas and that calculator. I've never looked back. I still occassionally dabble with HO 211 (one of my favourites) and HO 249 and even go so far as to do it the really old fashioned way with logs of trig functions, however, I still have no desire to go back. I find the formulas and a good calculator are the way to go.

Still, it is good to dabble with other methods just to keep sharp.

Robert

 

----- Original Message -----

From: jean-philippe planas <jeanphilippeplanas@YAHOO.COM>

Date: Tuesday, June 6, 2006 12:52 pm

Subject: Re: Reality check

> Of course if you use the formulas, you can use any start point, 
> one of which being your actual DR position. This start point 
> induces non rounded values for LHA and Lat.
>  JPP
> 
> Guy Schwartz <guyschwartz@SBCGLOBAL.NET> wrote:
>          When using HO 249 The assumed latitude is rounded and 
> the assumed Longitude is the number that will make the LHA an even 
> number (within the range of +/- 30 min. of the DR Longitude). When 
> plotting the assumed Lat and Long are used as the starting point 
> of the procedure. OK if I use the formulas:
>  Sin-1Hc = sin(dec) x sin(lat) + cos(dec) x cos(lat) x cos(LHA) 
> and Cos-1 (Zn)= sin(dec) - sin(lat) x sin(Hc) / cos(Hc) x cos(lat) 
> to calculate Hc and Z or Zn and then plot my position
>  wouldn't I be using the DR position as the start point?
>  Thank you,
>  Guy
> 
> 
> 
> 
> 
> JPP
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