The most useful class I ever took in secondary school was 8th grade
typing. We were taught to use two spaces between sentences. Like
this. But that was in the Dark Ages. I can't even remember when I
last saw an IBM Selectric typewriter. I don't use double-spacing
after sentences unless I am using a monospace font like this
Courier. The second space is not needed for clarity with
proportional fonts. Common word processing software can be set to
automatically correct your double spaces to one, or single spaces to
two, if you want. But inserting two spaces after sentences on this
forum is completely wasted effort, since the forum posting software
strips out the second space of normal text.
Like Chuck, I write my sevens with slashes. This is very useful for
people with bad handwriting. Once, I wrote myself a short note. A
week later, I could not read it. After two weeks, I still could not
read it, but realized it said "do the laundry." But I can always
read my sevens.