I hate when people cross me.
Oh, the perils of writing numbers…
I think the reason has to do with one’s degree of OCD. I am very compulsive. I have the diagonal tick =AND= underline on my 1’s, two horizontal ticks on either end of my capital I’s, never close off my 4’s (like this font does…it is SO gauche). I cross my 7’s AND add the downward tick. I slash my 0’s (for the number…)…it is all ridiculous, but if I don’t do it, people will not understand what is going on. Lesser mistakes have happened.
Not to digress, but MadSam makes a good point, too. So many places around the world write dates differently. Americans, I think, write Month/Day/Year; Japanese write them Year/Month/Day; Indonesians write Day/Month/Year…
I wouldn’t be surprised to find a Month/Year/Day format somewhere…
Now, what irkes me is when (like an expiration date on the back of an egg or something) is written with the 2-digit abreviated version XX.XX.XX, when, unless the number is greater than 12, you have NO IDEA what it is! I can never remember what country I’m in and which does which style. I say, if we’re not going to conform to one way (and I DON’T think we should anyway), to at least make sure everyone knows what we’re talking about…
Enough said on that, my head hurts, and I’ve got to hurry up and eat this peach before August 98th, 1923.
mike
As other posters have said, sevens are crossed in Germany (and the rest of Europe?) because their "1"s look like British / American "7"s. Uncrossed sevens just cause confusion here.
When I first moved here, workmates laughed at the foreign way I wrote my numbers: "Look at this! He writes his "7"s like "1"s and his "1"s like “I"s! Crazy Island Monkey!”
Of course, crossing your sevens in the UK or the US is just an affection to look all European, like asking for lemon in your tea, or asking for half a pint of froth on top of your beer. 
I’m afraid you’re wrong on that. The standard is to cross them. At least that’s what we’re taught in school.
I’ve been crossing my sevens and ones for as long as I can remember and that’s only when I don’t write them out in full. My zeds also get crossed and now that it’s been pointed out, I think I will start crossing my zeros.
Am I obsessive when it comes to writing? Let me put it this way, after a stressful day I will often sit down with pens and paper and practice my handwriting. I often have trouble with the lower case “r” as it looks like an “i” whenever I use a fine nibbed pen.
I will write out dates in full whenever possible and when I design forms I always put m d y under the / / as to reduce confusion.
My foreign co-workers found it strange that I wrote like this as it’s not typical for Canadians to do so and it is not taught in school here. It should be darn it.
My kids are adopting this practice as they learn to write… their written skills are still pretty atrocious and crossing their letters really helps distinguish them. Their skills have improved quite a bit since I gave them both fountain pens, using them requires a little more concentration on their part and they are pretty happy they have unique writing tools.
I put a great deal of importance on the hand written word and in my field, it is the primary method of communicating ideas and information. I have little tolerance for people who cannot write legibly and if they can’t write well, I will ask them to print. I’m told I have beautiful writing (for a guy), perhaps this is because I came from the old school where good penmanship was deemed essential.
Some late replies…
Just the way I heard it referenced. I surmise it’s to be taken as a short version of “upper mid-front rounded vowel” and the “lower mid-front rounded vowel,” which geometrically places you just ahead of the epiglottis. In any case your terms are far more accurate so please ignore my uninformed ramblings.
Really? I was told several times that I was being exotic. Same thing goes for writing the 9 as a q standing on the line and 8 as a slanted p with a closed loop at the bottom. Then again my mother crosses her 7s and she is very Swedish indeed.
Sparc