NavList:

Phil wrote:
"A simple example of what I'd like to do is to take an altitude (say) 62°30.2' and subtract a correction (say) 0.8' and get a result (say) 62°29.4' . This functionality seems to be available for time (at least as a HHMMSS) which is close but HH is limited to 24. Obviously I could go to Degrees and decimal degrees (DD) and just use as a decimal number, I just thought Excel might be smarter than that."

Yes, I see what you're saying here. You were hoping for "native" support of sexagesimal numbering, complete with the 20th century navigator's preference for DDmm.m (degrees and decimal minutes). No. That doesn't exist.

For everyone (not just Phil):
Celestial navigation is a tiny backwater, barely used by anyone. You have to use the tools that exist, and they are not built to satisfy minor communities. We have to "roll our own". That's why so many solutions were offered here. Far larger communities have to deal with similar issues. For example "hex" numbers or "hexadecimal" are widely used in coding and hardware/software design. If I want to add a number like "C4" to "FF2A01FA", I have to use conversion functions to go to decimal and back. The functions are at least internal in Excel (and its open-source clones), but there's no true native support even for something as common as "hex". Maybe even more remarkable is that Excel and its cousins have no support for trigonometric functions with degrees (decimal or otherwise!) as arguments. After all these decades, why can't I use a formula like =SIN(45°) instead of =SIN(RADIANS(45)) ...? [see my PS below]

The closest you can get in Excel to support for angles in degrees, minutes, and tenths is to create an "illusion" of built-in functionality by doing the conversion in and out of decimal "off-screen". You can either do this with VBA code (known for historical reasons as "macros"), or you can use cell formulas out in the "alphabet forest" (cells starting with AA, for example). This can be an effective solution if you need it, but it does have high "maintenance costs".

I don't recommend any of this. We can do all of celestial navigation with very few exceptions directly in decimal, and that's exactly what I have been teaching in my "Modern Celestial Navigation" workshops for years. Exceptions? There are no decimal sextants, as far as I know, so any sight you take will necessarily be given in degrees and minutes. Thus you have to do one "decimalization" right at the top (=deg+min/60). And sometimes, but not necessarily, it'a nice to have output in degrees and minutes. For example, if you're displaying an altitude meant to be compared directly with a sextant reading, or maybe just as a final option for plotting on some charts. Other than that, do the whole thing, beginning to end, in decimal degrees.

Frank Reed

PS: Doing the conversion back and forth from degrees to radians just to use trig functions is a huge nuisance, and in many software languages and tools like spreadsheets, there's a built-in function pair with annoyingly long names, like the RADIANS(x) and DEGREES(x) functions in Excel. These yield relatively unreadable cell formulas and code, and they do nothing internally than multiply and divide by a constant. My preference of long-standing is to drop the conversion factor into cell A1... =180/PI(). That displays 57.29... etc. Then I rename that cell to "kk". This is a handy trick, and if you don't know how, figure it out!! Now I can get my trig functions by converting back and forth, degrees to radians and radians to degrees in the usual way: =SIN(B3/kk) is the same as =SIN(RADIANS(B3)) but easier to type, easier to read, few parens to match up, and yields cleaner cell formulas. Or in the opposite direction, if I want the inverse cosine of some ratio, I can go with the built-in function and write =DEGREES(ACOS(B3/C3)) or I can write =kk*ACOS(B3/C3). Oh, and if you want to get a little more exotic with your formulas, you could rename cell A1 as Ω --or some other unicode character-- instead of kk.