I disagree. Banks of IF statements are real ugly and there are more elegant ways of doing the same thing, but those heaps of IF statements invariably outperform the more elegant solutions.

There is room for improvement, not in performance as in speed per se, but in resolution. You could almost interpolate steps of about a quarter of a degree (or better)... look...

if AD0 >= 446 then RA = 67
if AD0 >= 450 then RA = 68

You've got about four clicks or more...

if AD0 >= 535 then RA = 82
if AD0 >= 544 then RA = 83

between adjacent degrees... you have enough data to increase your resolution to beyond 1F. No, not with banks of IF statements this time, you need to be a little more creative with the math. If you can't figure it, come back and I'll show you how.