Mrs. ToKnow drinks Diet Coke and enjoys the idea of winning free money and swag, so we enter the codes under the caps to enter the drawings and stuff. I don’t usually find things to be designed with error-tolerance in mind, but I have to praise their system on this point: you can enter the character in the code that might be either a O or a 0 either way and it’s read as valid.
I used to slash my zeros, until I got a teacher who was very adamant that, even in handwriting, a slashed zero must mean the empty set.
I still fastidiously cross my handwritten “7”, “Z”, and “h”, put serifs on my “1” and “I”, and write “l” all squigly for clarity.
It does seem a bit persnickety. But, I have had students use the empty set symbol as shorthand for “no solution” or “undefined.” If you’re solving an equation, I need to be able to tell the difference between “the solution is 0” and “there are no solutions.” If you’re calculating the slope of a line, I need to be able to tell the difference between “the slope of this line is 0” and “this line has no slope (the slope is undefined).”
That’s what I remember thinking at the time. 
Of course, later, when I was an undergrad math TA, I was persnickety about students who’d say “x = undefined” or “x = ø” when the really mean “the solution set is empty”.
And phi, people, don’t forget the phi…
Yeah, this is just my own persnicketyness, arrived at by a combination of atrocious handwriting (but my written numbers are perfect, go figure) and computer science classes back in the day where you often had to write out by hand a code solution and it makes a big difference whether you’re using a letter O or a zero for a variable or function output or whatever–so slashed zeroes it became and still is for me.
Speaking of top serifs on the numeral “1”, I’ve noticed some Germans making the serif considerably longer than the main stroke, so the character looks more like a forward slash with a small vertical descender at the top. For a while I couldn’t tell if it was a “7” or a character I was not picking up on, like a Lambda or something. Somebody had to tell me it meant “one”.
I used a line printer once that slashed 0s. I often do it when writing stuff down that could be ambiguous.
But mostly I’m relieved. I thought this thread was going to be about doing away with 0s, and I came in to defend them.
You cross you h’s? Why?
BTW: You’re going to confuse physicists who read that as h-bar.
Oooħ, as a pħysicist, I want to do tħis.
As an undergraduate in physics, I got in the same habit. I cross z’s and 7’s and now I can’t not cross them, but somewhere along the line I lost the habit with zeros. I still cross my zeros when writing down passwords or any string that is a mix of alphabetics and numerics. (it has the double security role of confounding mathematicians that try to steal my password. :D). For obvious reasons, I never cross my h’s unless I intend a specific meaning.
It seems to me that someone who slashes their zeros could just use set notation to avoid the issue: use {} or { }. That’s what I use when typing, as it’s more easily available on the keyboard.
That said, I don’t think such is really all that useful, as mathematicians have noticed the ambiguity and thus tend to avoid using capital O. The only common exception I know if is in big-O notation for the time to complete an algorithm. But those have only a few fixed forms, and are easily disambiguated. Plus, in general, when are you going to write 0 times something? Just write 0.
As for the others: I used to cross z’s in math contexts only, but now I tend to use italic z’s (with the curved lines), same as you’re taught to use italic x’s. I’ve never crossed 7s, as I’ve been writing them with a serif since elementary school, as I just thought it looked better. (To this day, I look for seven-segment displays that have that extra vertical line.
Plus I almost never use that serif on the top of the 1, and, when I do, I include the bottom one. I write capital I’s with the serifs, and I curl my lowercase ℓ’s when they aren’t parts of words.
Seeing as I was unaware of the Scandinavian symbol, and had forgotten about the empty set, maybe the dot inside the zero would be less ambiguous. And my concerns stem more from people speaking to a computer, reading instructions, or other occasions when it is common to have someone say ‘O’ instead of zero.
You’ve cottoned on to my evil plan – to force physicists to use angular frequency instead of temporal frequency.
Back in the day when we wrote stuff out by hand we underlined the Os. If it wasn’t underlined, it was a zero.
I started slashing my zeroes in, I think, middle school. I got a math problem wrong because a hastily drawn six looked a lot like a zero, and I decided that slashing my zeroes would help eliminate the confusion.
I don’t slash zeroes unless numbers and letters are mixed together. If this is the case I add serifs and baselines to my ones, exaggerate the curves of my twos to avoid confusion with Zs, etc. However, I never slash my sevens as some people do.