NavList:

Never mind. I sent the last message without access to the tables and I had forgotten that there was the expected differences between H.O. 249 and H.O. 218 tabulated Hcs.

I did a more thorough comparison using H.O. 214 to look for the effect of rounding in both H.O. 218 and 249. Using all of the combinations for latitude 34 and declination of 19, I added the refraction correction from the Nautical Almanac to the values from H.O. 214 (which which are tabulated to one-tenth of a minute of arc) and found for all cases with Hc greater than 13 that they then totaled to the Hcs tabulated in H.O. 218 as expected. For Hcs of 10 to 13 adding the additional one minute of arc as required in the auxiliary table produced the correct value.

So it appears that H.O. 218, when the refraction correction is applied properly, produces the same computed altitudes as H.O. 249 which are also correct as rounded from H.O. 214.

gl
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