# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Basic celestial naviagtion using a scientific calculator**

**From:**Frank Reed

**Date:**2010 Aug 13, 16:32 -0700

David, you wrote:

" I have never used a scientific calculator before, but they don't look too difficult to master. However the two Casio calculators that I have, the Casio fx-82MS and fx-82w appear to only work in DDDMMSS.

Is there a way of entering DDDMM.M and getting answers in the same format? If this is not possible, are there any common calculators or iPhone/iPad apps which are useful for sight reduction calculations? As I want to get a good familiarity with the printed Nautical Almanac and sight redution tables, I am not lookiing for anything more sophisticated than basic arithmatic in DDDMM.M format."

If that's really all you want --just the arithmetic, as stated in your last comment here-- then I would recommend skipping the "DMS" function of the calculator altogether. It's no more and no less than a shorthand for a simple calculation:

(dd+mm/60+ss/3600)

For the case of decimal minutes of arc (and no seconds), it's even simpler:

(dd+mm/60).

So just do that! Assuming your scientific calculator has "parentheses" buttons for grouping calculations, when you get to any angle just enter it as above. For example, to convert 45d 12.5' to decimal degrees, key in "(45+12.5/60)" and you will get 45.208333. One little "gotcha": if you have an angle that should be interpreted algebraically as a negative angle, for example a south latitude, then you should change the sign after you close the final parenthesis. So suppose you need to calculate the product of the cosine of 45d 12.5' and the sine of 30d 45.7' South. You would enter this on the calculator as follows:

(45+12.5/60) COS * (30+45.7/60) PorM SIN =

[where I have written "PorM" for the usual "plus or minus" sign change key on the calculator].

Now, if you want something much more capable, there are a number of options available for handheld computers (devices known to the rest of the world as "smartphones") which I will describe in a separate post.

-FER

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