Skylark
Well-known member
No. In the Nautical Almanc GHA and Declination are in deg, min, decimal minutes format, as are Sextant angles, intercept and so on.
Calculator for angles expressed as decimal minutes?
- Thread starter Skylark
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Skylark
Well-known member
I agree with you, that’s why I’m looking for a calculator to simply help someone with the maths. As I wrote above, I do not want to recommend an App for the whole sight reduction process (for fear of making myself redundant ?).
AntarcticPilot
Well-known member
Thanks. Despite being very familiar with the maths and theory of sight reduction, I have never actually needed to do it for real!! I could do it from first principles, no problem (I can't do rote methods) but never actually have.
Skylark
Well-known member
I get your point and you’re lucky to be able to “see and read” maths. I graduated in engineering in 1978 and can also reduce a sight without problem from first principles. I don’t see the point of using a Template but I’m acutely aware that many do, hence I teach their use. I’m trying to put myself in the position of someone who does not “get” maths. A surprising number of people either struggle or make silly errors in adding and subtracting angles, hence it would be helpful for them to have a calculator with the commonly used format. Alas, no luck as yet…….
capnsensible
Well-known member
It's not as complicated as people try to make out.
Get sight. Fill in pro forma. Do some adding up and taking away. Hey presto, position line.
I think people get put off not realising how simple it is.
capnsensible
Well-known member
Have been in contact with our guy who is now Chief Mate on Superyachts.
He can't remember either! But he did say it took him around 10 minutes to find on Google playstore.
AntarcticPilot
Well-known member
I've had to do considerable similar maths professionally, as post-processing navigation data and handling map projections was everyday stuff for me. So computing the azimuth and distance from a nadir point to a DR position and then using the sight to compute the offset along the azimuth is conceptually pretty straightforward by comparison!
Frank Holden
Well-known member
Thats the way we used to do it when I had a day job - for the first 20 years at least.
Rule up my sight book every morning and then take the sight.
Haversine formula is actually easier than either air navigation tables or calculator.
Simple addition - OK maybe having to subtract to get L~D.
Hard bit that I don't miss was the day's work (right hand page) involving mercator sailings and traverse table. We weren't - in my early days - allowed to use plotting sheets - never even knew they existed until I went 'foreign flag'.
Simple tip for subtracting degrees - convert the last degree of the larger number to minutes. Simple case - if wanting to subtract 312º 19' from 360º just write 359º 60'. Easy peasy.
Another tip. If only using a single page of your sight book each day ie you are doing all your plotting of P/Ls and runs on a plotting sheet - use right hand page and then left hand page. Makes it a breeze to carry any workings forward. Hard to explain but easy to do.
The £42/18/2? Dunno what thats doing there - but looks like a month's pay for a 4/0.
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Skylark
Well-known member
Thanks for taking the trouble to ask. I’m evidently lacking in search criteria skills because I can’t find one on either Google or Apple App Stores ?
The only screen I’ve seen which adds and subtracts and gives answers in the deg, min, decimal min format is embedded within an App called Star Pilot. This is a celestial navigation App which defeats the point of doing a manual sight reduction.
Otherwise, I do not believe that a pocket calculator exists that gives output/answers in the deg, min, decimal min format.
Frank Holden
Well-known member
What used to exist about 30 years ago were the Sharp PC-1403/PC-1246 and Casio FX-720P and 730P. They could be programmed to do the whole sight reduction. They output answers in deg.min.decimalmins.
I had Sharp, great bit of kit when you also had the Mike Harris book 'Astro Navigation by Pocket Computer' to program it with.
Maybe the OP's student, instead of employing mental arithmetic, could use the wrinkle I mentioned up thread above along with pencil and paper?
I had Sharp, great bit of kit when you also had the Mike Harris book 'Astro Navigation by Pocket Computer' to program it with.
Maybe the OP's student, instead of employing mental arithmetic, could use the wrinkle I mentioned up thread above along with pencil and paper?
Skylark
Well-known member
Thanks @Frank Holden. There are a few ways that I have in mind to try, including your much appreciated suggestion.
Just to show that I’m not completely crazy in wanting this format on a calculator, here’s a screen grab from the App I mentioned above.
Just to show that I’m not completely crazy in wanting this format on a calculator, here’s a screen grab from the App I mentioned above.
benjenbav
Well-known member
Hi - there’s a free app on Apple called, bewitchingly enough, Celestial Nav. Defaults to MS but in the settings menu you can choose decimal minutes, although you have to upgrade to the pro version (£10 p/a - I think) in order to access this setting). Hope this helps.
Skylark
Well-known member
I've just downloaded the free version to take a look. As you rightly say, the pro version is needed in order to change units. The free version asks for AP Long as input. It also derives Ho from Hs so the user doesn't manually have to correct for index error, dip, parallax and semi diameter. It then gives Intercept as an output. These are generally where the adding and subtracting takes place but this App does it for you. Looks quite easy to use but not really what I'm looking for albeit I appreciate that you've taken the trouble to post, thank you.
[194224]
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The Casio you mention can’t natively display in the format you want as you know but it can do the calculation based on input in form DDD° MM.mm’. It does mean therefore to get the answer you’re looking for you need to carry out one extra step.
Is it as neat and intuitive as an app or something that can handle the format you require? – No. Also adding a step does introduce another opportunity for error. You may have settled on a workable solution by now but just for the sake of it here is an example of how it could be done.
Say we want to do the calculation:
50° 10.5’
+ 9° 56.75’
° ‘ “ < below, this means press the key so marked
Do the calculation as normal, enter the following noting that the calculator requires you to enter the minutes even if zero
50 ° ‘ “ 10.5° ‘ “ 0 ° ‘ “ + 9 ° ‘ “ 56.75 ° ‘ “ 0 ° ‘ “ =
The following is displayed: 60° 7’ 15”
But you need it in decimal minutes so you need an extra step.
Write down the degrees and minutes as you would anyway (60° 7’), make a note of the seconds (15).
The extra step is just to enter the minutes and divide by 60
15 ÷ 60 = giving 0.25 and add that to the answer you have giving 60° 7.25’
Not as tidy as it could be and perhaps not the answer you want but it does work.
Is it as neat and intuitive as an app or something that can handle the format you require? – No. Also adding a step does introduce another opportunity for error. You may have settled on a workable solution by now but just for the sake of it here is an example of how it could be done.
Say we want to do the calculation:
50° 10.5’
+ 9° 56.75’
° ‘ “ < below, this means press the key so marked
Do the calculation as normal, enter the following noting that the calculator requires you to enter the minutes even if zero
50 ° ‘ “ 10.5° ‘ “ 0 ° ‘ “ + 9 ° ‘ “ 56.75 ° ‘ “ 0 ° ‘ “ =
The following is displayed: 60° 7’ 15”
But you need it in decimal minutes so you need an extra step.
Write down the degrees and minutes as you would anyway (60° 7’), make a note of the seconds (15).
The extra step is just to enter the minutes and divide by 60
15 ÷ 60 = giving 0.25 and add that to the answer you have giving 60° 7.25’
Not as tidy as it could be and perhaps not the answer you want but it does work.
Skylark
Well-known member
Thanks @Baltika_no_9 kind if you to put so much effort into a response.
I’ve pretty much given up on finding a calculator to the required format ?. I’ll see how the guy in question approaches what for many is straightforward mental arithmetic. I’m hoping that he’s over played his concern regarding dyslexia and that, with a bit of help, he’ll be fine. His course starts at the end of next week.
I’ve pretty much given up on finding a calculator to the required format ?. I’ll see how the guy in question approaches what for many is straightforward mental arithmetic. I’m hoping that he’s over played his concern regarding dyslexia and that, with a bit of help, he’ll be fine. His course starts at the end of next week.
Frank Holden
Well-known member
Usage of the term 'mental arithmetic' may have changed since i was a pup but I thought it involved doing calculations 'in your head' without benefit of pencil or paper.
I can't say I would ever consider doing any part of sight reduction in my head - OK some of the little bits of interpolation .
Pencil and paper leaves a record of your workings so that - if you find yourself in Salisbury Cathedral - you can go back and find where you went wrong.
Adding degrees =
50º 10'.5
+9º 56'.7
-------------
59º 67'.2
=60 º 07'.2 ( OK I used mental arithmetic for that last bit
. )
Subtracting =
50º 10'.5
= 49º 70'.5
- 9º 56.'7
--------------
= 40º 13'.8 ( check by adding answer to the number you subtracted - OK I know it has a fancy name - using mental arithmetic if you so choose.)
Quicker -and cheaper- than using a calculator.
I can't say I would ever consider doing any part of sight reduction in my head - OK some of the little bits of interpolation .
Pencil and paper leaves a record of your workings so that - if you find yourself in Salisbury Cathedral - you can go back and find where you went wrong.
Adding degrees =
50º 10'.5
+9º 56'.7
-------------
59º 67'.2
=60 º 07'.2 ( OK I used mental arithmetic for that last bit
. )Subtracting =
50º 10'.5
= 49º 70'.5
- 9º 56.'7
--------------
= 40º 13'.8 ( check by adding answer to the number you subtracted - OK I know it has a fancy name - using mental arithmetic if you so choose.)
Quicker -and cheaper- than using a calculator.
[194224]
...
I take your point Frank and agree with you on the benefits and simplicity of the pencil and paper method. The OP though is trying to offer a solution for someone who may have difficulty with mental arithmetic but even pencil and paper requires the person to use mental arithmetic. Taking your subtraction example, for the minutes part we have 70.'5 - 56'.7 yielding an answer of 13'.8. The manipulation required to arrive at 13'.8 is not shown on your (electronic) paper, you did it in your head. If someone is genuinely impaired, then that might be difficult. The paper records the problem and the solution but it does not demonstrate how the answer is derived. I can write a trivial problem down, say, 9-7 but before I can write down the answer I need to do the subtraction in my head. Just writing 9-7=2 doesn't avoid mental arithmetic. To avoid mental arithmetic completely and assuming I can count then I might make 9 marks on the paper then cancel 7 of them and count the remainder. That shows how I arrived at the answer. Otherwise the manipulation needs to be done in the head. The OP's search for an alternative method by calculator or otherwise eliminates all the mental burden.
Edit
It's worth remembering what the OP is trying to achieve; to help someone with the sight reduction process. The person will already be using pencil and paper - a sight reduction form of some sort but that does not help. There are several points during the process where sexagesimal arithmetic is called for dealing with either time or angular distance. The person is presented with a problem like the ones in your post, say adding two angles. The problem is finding C given that A+B=C. A and B are there, written on the paper but if the person is not as confident or as able as you are to perform that addition mentally then an external aid is required. It's that aid the OP is looking for. Having a pencil doesn't help if you can't manipulate the numbers in front of you. That aid might be a calculator for instance.
You could use the pencil to press the buttons of course
Edit
It's worth remembering what the OP is trying to achieve; to help someone with the sight reduction process. The person will already be using pencil and paper - a sight reduction form of some sort but that does not help. There are several points during the process where sexagesimal arithmetic is called for dealing with either time or angular distance. The person is presented with a problem like the ones in your post, say adding two angles. The problem is finding C given that A+B=C. A and B are there, written on the paper but if the person is not as confident or as able as you are to perform that addition mentally then an external aid is required. It's that aid the OP is looking for. Having a pencil doesn't help if you can't manipulate the numbers in front of you. That aid might be a calculator for instance.
You could use the pencil to press the buttons of course
Last edited:
Frank Holden
Well-known member
What I have seen people do is write tiny little numbers down as they are doing the work on paper. Difficult to explain but I think it goes thus. Lets say subtracting 167 from 252 . Within their head ' seven from two doesn't go, seven from twelve is five - carry one' . Writes little '1' next to the '6'. In head 'One plus six is seven - seven from five doesn't go - seven from fifteen is eight carry one ' writes little '1' next to '1'. Two from two equals zero, answer is eighty five.
Confession time - I couldn't use a scientific calculator to save myself.
Confession time - I couldn't use a scientific calculator to save myself.
[194224]
...
I have to admit I still do that! It's quite similar to what you did in your example by reducing the degree number by one and adding 60 to the minutes column. It, for me and possibly others, does simplify the arithmetic.
mjcoon
Well-known member
I believe that breaking pencils is one of the standard stress-relief actions...You could use the pencil to press the buttons of course