Originally Posted by sputinc7

Maybe so, but a general idea is all we really need... Where do we even find those 890 values for our mathematical adventure, anyway? I don't have time for all that, and I have more time than most people, other than retired folks, I guess.
Where I live is 9b but my house is in a spot where the overnight lows are routinely 5-7 degrees cooler than other nearby areas, and I quickly figured that out and keep it in mind. So, when they say the low will be 43, I know 36 or so is much more accurate and act accordingly. There won't be frost at 43, but there will be at 36.(Assuming the dewpoint is at or above that and winds are calm)