DM 41X an emotion, or an ordinary calculator.

Discussion around the SwissMicros DM41X calculator
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Ancient Sailor
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DM 41X an emotion, or an ordinary calculator.

Post by Ancient Sailor »

Today, for the third time, I received the flat cardboard box from Switzerland containing the DM41X.
When unpacking it, an emotion came over me, which I did not have with the DM15L and the DM42.
It came from the realisation that the HP41CX was never designed to be an ordinary calculator. It has become a life-long journey. I have been ashore for 3 years now and thought will never again shoot a navigation star for a position on earth. But I will give the DM41x a chance to honour the magic of classic navigation.
To all who made this possible, thank you for making this DM41X a beautiful and worthy successor to the HP41CX.

Kind regards
Rupert Van Swol
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dm319
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Re: DM 41X an emotion, or an ordinary calculator.

Post by dm319 »

Have you given the DM41X the opportunity yet?! I'd be very interested in an explanation of how you'd calculate position using the ?sextant and your calculator.
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rudi
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Re: DM 41X an emotion, or an ordinary calculator.

Post by rudi »

Ahoy Ancient Sailor, happy to see a fellow sailor ;-)

I bought my first HP, a HP-41CV with a Navigation pack in a Target store in Charleston in early 1983, when I was there as a cadet.
My trusty HP-41 followed me at sea until I went ashore and studied electrical engineering in mid 90's
I had great use of the deadreconing programs and also the astronomical navigation pack. Made astromical navigation so much easier, especially for the Moon and planets.

I also wrote several maritime programs. The one I used the most, was a "Plotter", where You could enter bearing/range/time for targets (up to 20 I think), and from the current time, and own vessel SM and CMG, the program could calculate CPA, TCPA and also calculate a new course at a specific time, to increase CPA for any vessels comming too close. This was before ARPA's got common on commercial ships.

I have sold ( :shock: :roll: ) my HP-41 CV and all the modules, magnetic tape, magnetic card, CRT monitor and a lot of other stuff long ago. But I have the program on paper somehere in an old Danish HP magazine.

I also made a sun rise calculator, and moon rise, I even think I ported that to the HP-42S I bought in the 90's

I also think of getting a DM41 just for the nostalgic reasons ;-)

Nice to hear from another sailor here on this forum!
/Rudi

DM-42 (s/n 06999), HP-42S, HP-35s, HP-11c, HP-32SII (ex HP-41CV, ex HP-75C, ex HP-48G + a lot, really lot of a accessories)
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rudi
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Re: DM 41X an emotion, or an ordinary calculator.

Post by rudi »

dm319 wrote:
Tue Aug 09, 2022 10:15 am
Have you given the DM41X the opportunity yet?! I'd be very interested in an explanation of how you'd calculate position using the ?sextant and your calculator.
I could explain you that on the back of a napkin, faster than you could finish a pint of beer ;-)

Basically, you measure a star's altitude and also calculate the altitude it should be at, if You were at an estimated position at the observation time.
The difference in the observed height and the calculated height, is the distance along a line towards or away from a point directly below the star.

By making seleral such observations in different directions, You end up with a bundh of lines, that in theory should cross in one point, but off course, they done due to inaccuracy. But with a little training and an accurate chronometer, you can determine your position within a few hundret yards.

Off course, the above is extremely simplified, you also have to take into account that your ship is moving during the observations, that could be over 10-20 minutes, the atmospheric refraction, parallax error on the moon (if observing the moon), the semidiameter of the sun/moon (their angular sizes varies a lot), the drift of the chronometer, your height above the sea surface, and much much more I dont quite recall ;-)
/Rudi

DM-42 (s/n 06999), HP-42S, HP-35s, HP-11c, HP-32SII (ex HP-41CV, ex HP-75C, ex HP-48G + a lot, really lot of a accessories)
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dm319
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Re: DM 41X an emotion, or an ordinary calculator.

Post by dm319 »

Having not had to geolocate myself at sea using the stars I feel I haven't really lived! I presume you need a reading off the horizon? If so will that be affected by the tide/swell of the sea? I read a book called 'longitude' and have been to the museum at Greenwich. Both fascinating.
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rudi
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Re: DM 41X an emotion, or an ordinary calculator.

Post by rudi »

dm319 wrote:
Fri Aug 12, 2022 11:05 pm
Having not had to geolocate myself at sea using the stars I feel I haven't really lived! I presume you need a reading off the horizon? If so will that be affected by the tide/swell of the sea? I read a book called 'longitude' and have been to the museum at Greenwich. Both fascinating.
The tide/swell does not have any significant effect. The celestial bodies height are measured from the horizon. And even without a horizon the height can be measured from an “artificial horizon” (a small bowl of mercury) - this takes quite some practice and is mostly done in daylight (sun or moon.

And yes - I have also been at the Greenwich museum several times. Fascinating. I can recommend reading the book by Dava Sobel “Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time”i
/Rudi

DM-42 (s/n 06999), HP-42S, HP-35s, HP-11c, HP-32SII (ex HP-41CV, ex HP-75C, ex HP-48G + a lot, really lot of a accessories)
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redglyph
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Re: DM 41X an emotion, or an ordinary calculator.

Post by redglyph »

rudi wrote:
Fri Aug 12, 2022 11:36 pm
The tide/swell does not have any significant effect. The celestial bodies height are measured from the horizon. And even without a horizon the height can be measured from an “artificial horizon” (a small bowl of mercury) - this takes quite some practice and is mostly done in daylight (sun or moon.

And yes - I have also been at the Greenwich museum several times. Fascinating. I can recommend reading the book by Dava Sobel “Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time”i
I was wondering about that, so you can find enough information from the Sun (and possibly the Moon if it's over the horizon) to estimate your position in daylight?

Is the current and the drift due to it relatively constant? I suppose it's the case when you're far enough from the coast but I have no idea.

My only experience in navigation is from a plane and inland, so it's not difficult to find landmarks and calculate the drift. Though using a calculator would be hard, so we usually do that with a few calculation tricks and approximations. For the exams anyway, most are using a GPS because it's much easier and removes a lot of burden; there's already a lot to do. The general idea remains the same though, and they did use sextants in aviation too (for instance there's a small dome window on the top of DC-6 and Constellation L-049 planes for that purpose). I've always found interesting that there were so much in common between seamanship and aviation.
ecsfang
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Re: DM 41X an emotion, or an ordinary calculator.

Post by ecsfang »

redglyph wrote:
Thu Aug 18, 2022 11:00 am
I've always found interesting that there were so much in common between seamanship and aviation.
You could also include astronautical ...
The astronauts during the Apollo missions also included a sextant (in a more modern form ;)) for navigational purposes.
So drifting on the way to the moon, they could keep track of their position using the same old method, still valid in space as on the sea or in the air!

See eg. The story of the Apollo sextant

Cheers,
Thomas
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redglyph
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Re: DM 41X an emotion, or an ordinary calculator.

Post by redglyph »

ecsfang wrote:
Thu Aug 18, 2022 1:57 pm
You could also include astronautical ...
The astronauts during the Apollo missions also included a sextant (in a more modern form ;)) for navigational purposes.
So drifting on the way to the moon, they could keep track of their position using the same old method, still valid in space as on the sea or in the air!

See eg. The story of the Apollo sextant

Cheers,
Thomas
That's quite interesting. Those guys were very resourceful (and courageous)!

But I didn't mean the sextant specifically, which merely anecdotal in aviation. But the law, the terms, the measurement units and the methods are very similar. I don't know details about navigation in space but I'd expect they had to reinvent pretty much everything.
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