'Way back then, when dinosaurs strode the earth and System/360 reigned
supreme, we were taught to slash our zeros and sevens (can't quite find
the glyphs for them right now) in order to distinguish them from Oscars
and Ones for the benefit of the keypunch girls...'
I slash both zeros and sevens too. With regards to the zero I learned it at the
university in the 70ths,
however I believe that slashing sevens I learned already in the school days(60ths) or even
at home
by my parents (50ths).