I looked at the butkus site and read a few instruction manuals for early Weston meters. The manuals tell you to exclude the sky.
Now I have to concede a point.
I no longer think that averaging light meters were designed to read a statistically average scene brightness distribution.
If the arrow pointed to average scene brightness distribution like I have been saying all along -- you wouldn't have to exclude the sky. So I must be wrong.
It sounds more like the instruction manuals were written to explain how to use something in a way it wasn't originally designed.
I work for Kodak but the opinions and positions I take are not necessarily those of EKC. Especially on this thread.
p.s. It's amusing that Weston company proudly explains ASA standards for film speeds were based in part on their research, but the standards changed just enough that ASA speeds and Weston speeds don't match.
p.p.s. I would be very amused if it turned out ASA standard meter calibration point was based in part on Weston meter calibration research but changed 18% to 12%.