I learned to write by copying the font from my mother's high school typewriter, built in the 1920's it was older than she was.
There was no numeral 1, it was unnecessary since people just used the lower case L.
My first variable.
But my font was way out of date even for that distant decade. Looked older than newsprint of the time.
Anyway, when I got to school it was easy to learn printing the blackboard way, and some of us then did cursive writing and were promoted to third grade at the end of the year.
So for the good part of a year I did cursive but before the next September they closed that school.
It was like getting a promotion but the employer still closes beyond your control before you can even get into duty.
Well instead I had to go to a place where they would only put me in second grade since they didn't want me to be so much younger than the other kids. They did not do any writing their first year and were just going to start printing with the big pencils. There would be no cursive allowed until third grade so I went back to a year of printing instead of handwriting. It was easy to see that conformity took precedence over advancement in such an institutional environment. By the time I got to third grade I could already print faster than many adults could do longhand, I was not going back to my slow cursive, and I made it perfectly clear that I was already more advanced when I got there a year earlier. Not an encouraging academic experience, but seemingly common.
It evolved into a form of fast printing eventually toward what looked like shorthand with hieroglyphics, not readable by others at all. I still change fonts all the time.
There are no remaing samples of my actual handwriting.
So that's why my handwriting sucks. It doesn't even exist any more.
However numbers need to be so unmistakeably readable when a lot is at stake, letters too but I start with numbers.
Naturally I used the same character (a straight line) for 1 and lower case L for the longest time, even though I had started with serifs on upper case i and thoroughly dotting my lower case i's to avoid confusion. Eventually all lower case L needs a little tail. Turns out to be the lower case L is the one I could actually do without. Gotta have numbers.
Basically, I encourage conscious calligraphy or "lettering" (drafting room or comic book style) in notebooks and documents. In an international laboratory you really don't want a trailing numeral 9 being confused for a lower case G meaning grams.
With cultures that cross their 7, consistency is important since often there is also an upstroke on the 1 which can throw those off who are unfamiliar. Shortening the upstroke can be a good move but you want data recording to come naturally and not require conformity for its own sake. I use an uncrossed 7 with a bold serif but not wild enough to ever be confused with a 9 myself. 4 must never be confused with A or 9, nor 8 with B, or 5 with S. Zeros are good crossed when it might be helpful. Stuff like that. It must make sense.
I never want to make people feel like bureaucracy is more important than the characters they are working with. Not a good feeling at all.
If your handwriting sucks because it's difficult for others to read or decipher, then in that case consider it a special occasion and use calligraphy.