>>134513466) Any fountain pens at all. I wouldn't use them for any non-proof work. In fact, I'd say to not use them for mathematical work at all. They simply aren't suited for the mentality associated with math, unless you're enough of a genius to perceive some kind of invisible horizon into which blend all human structures, in which case more power to you. In such a scenario, you already know to use a vintage gold nib, as the methods of alloying that were previously common are no longer economically feasible, leading modern fountain pen nibs to be lacking in that subtle spring that gives perhaps the best portion of the experience of use. I would recommend using Waterman ink if you're a mathematician, and Diamine if you're an engineer. If you're a hobbyist, Noodler's is the way to go. Iroshizuku is overpriced.
7) Rotring-branded items. Rotring is a highly overpriced brand, like most German stationary, but they make quality products. Do not attempt to use a Stylographic-tipped pen without prior experience, as they use a flat-cut tip as opposed to a round-cut. They have the best mechanical pencils on the market.
8) Retro 51. Don't.
9) Vintage stylographs. The patricians choice, preferable in ebonite orange or black, carrying old chemical smells almost certainly carcinogenic. Be prepared to do some work to get them operating properly, temperamental bitches that they are.
10) Bic. The based normie option. Not actually that bad, just leave an unclean line, like all ballpoints.
Finally, don't listen to anybody who tells you to use a G2. They have the worst quality control on any name-brand gel pen I've ever used. The Signo 207/307 is barely above it; oddly enough, the micro is more consistent than the 0.7mm, and the 207 more than the 307.
t. Pen Autist from /lit/