Maybe it is. However, clear or not, I've more than once found errors in
Wikipedia, so I'd regard it as a guide to what is probably correct rather
than a reference.

I agree. But usually Wikipedia also contains references to the
original sources (this is what the editors strive to). In this
case CENELEC Harmonisation Document HD 472 S1:1988, ANSI
C84.1 and BS 7697.

Julf