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    Re: Dennert & Pape MHR-1 Dennert & Pape MHR-1 HR-2
    From: Gary LaPook
    Date: 2013 Jan 27, 22:42 -0800
    I find it surprising that neither Bygrave or Dennert & Pape came up with a method for dealing with the situation of the body's declination being within 20 minutes of zero since this situation exists for the sun (the most important body) for two days in the spring and two days in the fall, four days out of 365 days a year. My method was not hard to discover and provides accurate results for this situation so it s a mystery to me why similar instructions were not provided with these instruments. Without providing such a procedure navigators would need to learn and carry a complete other celestial computation method to be able to operate each day of the year.


    --- On Sun, 1/27/13, Hewitt Schlereth <hhew36@gmail.com> wrote:

    From: Hewitt Schlereth <hhew36@gmail.com>
    Subject: [NavList 22143] Re: Re: Dennert & Pape MHR-1 Dennert & Pape MHR-1 HR-2
    To: garylapook@pacbell.net
    Date: Sunday, January 27, 2013, 6:48 PM

    Brad -
    I will defer to Wolfgang, but my translation of
    Bei stundenwinkel und deklination zwischen 0 und 0 20 sowie bei
    stundenwinkel 90 ist der Hohenrechenschieber nicht zu verwenden
    For hour-angle and declination between 0 and 0 20' as well as for hour-angle of 90, the altitude slide is not to be used.
    The two dots above the o are called an umlaut (Höhenrechenscheiber). The ö sound is made by shaping your lips as though you were going to say 'oh', then trying to say 'ee'.
    Sent from my iPad
    On Jan 27, 2013, at 4:11 PM, "Brad Morris"  wrote:
    > Hi Gary
    > On the inner tube of my MHR1 (noted as tube II in the German instructions &
    > also the scale upon which we set the declination), the minimum angular
    > dimension is 20 min (179 deg 40 min).  At the other end of this same scale
    > I find 89 deg 40 min (90 deg 20 min).
    > Tube I (outer tube, upon which in the first step we set zero, or in the
    > third step, upon which we set azimuth) starts at zero.  The other end of
    > tube I is marked 89 deg 40 min (90 deg 20 min).  The double markings begin
    > at 35 deg (145 deg).  Below 35 deg, there is only a single mark, obviously
    > just due to limited room.
    > I thought to mention this as your email indicates that the smallest angular
    > dimension on this scale is 30 min.  Not true for mine.  I simply don't know
    > about others.
    > There ARE special instructions (in German) for when "stundenwinkel" (t)
    > and "deklination" are between 0 and 0 deg 20 min.  I cannot read German.  I
    > include the text following.  All typo's are mine.
    > Bei stundenwinkel und deklination zwischen 0 und 0 20 sowie bei
    > stundenwinkel 90 ist der Hohenrechenschieber nicht zu verwenden.
    > The first 'o' in Hohenrechenschieber has the two dots above it.
    > Regards
    > Brad
    > On Jan 27, 2013 6:39 PM, "Gary LaPook"  wrote:
    >> ------------------------------
    >> 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-flight-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 1º.
    >> 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 0.9º 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 85º 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-Bygrave-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
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    >> ----------------------------------------------------------------
    >> View and reply to this message: http://fer3.com/arc/m2.aspx?i=122013
    >> *Attached File: 122138.calcul de navigation, v2 (courante).pdf 
    >> *
    >> *Attached File: 122138.bygrave manual.pdf 
    >> *
    >> View and reply to this message: http://fer3.com/arc/m2.aspx?i=122138
    > View and reply to this message: http://fer3.com/arc/m2.aspx?i=122139

    View and reply to this message: http://fer3.com/arc/m2.aspx?i=122143

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