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Bill,
You changed one too many ones to twos when you edited the formula:
toward the end, you've got "INT(B2)+2" where it should be "INT(B2)+1".
That seems to be the only problem.

You wrote:
"Note: "INT" in my Excel rounds down the nearest integer."

This you can count on. INT(x) goes back to the earliest programming
languages. By contrast, VLOOKUP(x,a,i) is a relatively modern addition
to spreadsheet functionality so you have to double-check the way it
works.

And you asked:
"As a follow up, what is your opinion of the Saemundssen quoted in
Meeus for Hc to H (below) as opposed to 57"/tanH"

Well, I'm not quite sure what you're asking here. Those are not used
for the same purpose. One thing to remember: equations like the one by
Saemundssen that you mentioned are not "derived" from anything.
They're just numerical "fits" to the tabulated data. Somebody just
monkeyed with a simple equation and adjustable parameters until the
equation's ouput looked like the table, more or less. If you have the
table, you should *never* use those fitted equations. Likewise, if you
have entered the table into a computer and implemented code or a
spreadsheet function to interpolate, then you would always prefer that
to an equation like Saemundssen. By contrast, the short equation for
refraction above 15 degrees (r = 57"/tanH) is derived from fundamental
physics given certain limiting conditions so we know *exactly* where
it begins to be inaccurate (at some specified level of accuracy).

-FER


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