# NavList:

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

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Re: Moon total correction- round it up?
From: Frank Reed
Date: 2014 Oct 10, 08:56 -0700

Sam, you wrote:
"I never said my sextant reads to seconds. Read the original post."

It's not clear at all in your original post where you got these numbers with seconds of arc in them. What is clear in many of your posts is that you do not fully understand the concept of "significant digits" or "accuracy and precision". These are basic mathematical concepts that you will benefit from. Unfortunately, as we discussed previously, if you are actively opposed to mathematical concepts, you will be somewhat "crippled" in your explorations of celestial navigation. There's plenty that you can learn by rote and by rule, but you still need some mathematical "common sense".

"Hs= 43d 43.4min
IE -.1
Result divided by 2= 21d 51min 39sec (that's what the calculator says)"

Your result goes beyond the "precision" of your input and beyond the "accuracy" of your observations. You need to learn when you can drop digits. How accurate is your sextant? What is the magnification of your telescope? Just because you can read the micrometer to tenths of a minute of arc (its "precision") does not mean that the instrument (and observer) are accurate to tenths of a minute of arc.

More generally, dividing an angle by two is absolutely something that you should be able to do without consulting a calculator. There are only two cases you need to worry about when halving an angle. Consider as examples of these cases the angles 42° 17.5' and 43° 19.8'. Can you divide those by two in your head (or at most with a pen and a bit of scrap paper)?

-FER

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