NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Dennert & Pape MHR-1 Dennert & Pape MHR-1 HR-2 Cylindrical Slide LineRuler
From: Wolfgang Hasper
Date: 2013 Jan 30, 20:54 +0100
From: Wolfgang Hasper
Date: 2013 Jan 30, 20:54 +0100
Gary, thaks for poining me once more to your paper. I did not realise how completely you have described ways around all conceivable special cases. Great! I will prepare an additional label for the outer tube in the MHR1 style to have your rules always at hand. Best Wolfgang Am Montag, 28. Januar 2013 00:38 schrieb Gary LaPook: > Do you have any actual instructions for using your > MHR-1 for dealing with the special case when the > declination is less than the lowest� declination > marked on the tangent (or co-tangent) scale, 20' for > the Bygrave and 30' for the MHR-1 and 50' on my flat > Bygrave? I have never been able to find instructions > for this situation. I am attaching a description for > the use of this instrument (in French) which says it > is "inutilisable" for this situation and the > original Bygrave instruction manual is silent as to > this situation, also attached. > > I came up with a method of dealing with this > situation and it is posted on my website at: > https://sites.google.com/site/fredienoonan/other-fli >ght-navigation-information/modern-bygrave-slide-rule > > (In my notation "W" is the same as "y" in Bygrave's > notation and "x" on the MHR-1.) > > "When declination is less than one degree you can't > begin the computation the normal way to find "W" > because you have to start the process with > declination on the cotangent scale and this scale > doesn't extend below 1�. So in this case you just > skip the computation of "W" and simply set "W" equal > to declination. Using this method you arrive at an > azimuth that is not exact but is a close > approximation and in the worst case I have found the > azimuth is still within 0.9� of the true azimuth but > most are much closer. If the declination is less > than one degree and the latitude is also less than > one degree, follow this procedure and also assume a > latitude equal to one degree. After you have > computed the Az you then follow the same procedure > discussed above for azimuths exceeding 85� by > interchanging the latitude and declination and then > computing Hc which will produce an exact value of > Hc." > > Also see my prior post at: > > > http://fer3.com/arc/m2.aspx/Computing-azimuth-with-B >ygrave-special-cases-LaPook-feb-2010-g11826 > > gl > > > > --- On Sun, 1/20/13, Marc Giordan >wrote: > > From: Marc Giordan > Subject: [NavList 22013] Re: Dennert & Pape MHR-1 > Dennert & Pape MHR-1 HR-2 Cylindrical Slide > LineRuler To: garylapook---net > Date: Sunday, January 20, 2013, 11:08 AM > > Sir, > I am French and also quite familiar with the use of > the MHR 1 at sea (I used it for 2 atlantic crossings > by sail) Would any one wish to be trained in using > it, I am ready to help ! The MHR 1 was bought by my > father some 30 years ago at the flee market in Paris > Yours > Marc Giordan > 26 rue de Paris > 78560 le Port Marly > (0033)675210703 > ---------------------------------------------------- >------------ NavList message boards and member > settings: www.fer3.com/NavList Members may > optionally receive posts by email. To cancel email > delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------- >------------ > > : > http://fer3.com/arc/m2.aspx?i=122013 > > > Attached File: http://fer3.com/arc/img/122138.calcul > de navigation, v2 (courante).pdf > > Attached File: > http://fer3.com/arc/img/122138.bygrave manual.pdf > > > : > http://fer3.com/arc/m2.aspx?i=122138