There is a calculation involved....depending on where on earth a reading is taken, and what time of year. I'll begin working on that....
Yeah, that calculation looks pretty complex. I see that your maximum sun height today is only 44.2 degrees. http://aa.usno.navy.mil/cgi-bin/aa_altazw.pl That could make a big difference. The sine of 44.2 is .697, but I doubt the relationship with total UV is linear. I would like to see what you get throughout the day. I assume it would zero out just after sunset