I'm the author of a custom chemistry keyboard on iOS. I am looking at improving the selection of Unicode arrows I can provide. When the device is a phone in portrait mode, I don't have a lot of extra room on screen, so I give a flyout with:
→, ⇌, ↔, ⇢, ↛
When the phone is rotated or it's on a larger device, I have some extra room, so I was thinking about adding either more items in that flyout, or perhaps another button with an expanded set. Maybe something like:
⇄, ←, ↝, ↮⟿
I would like to make the most useful unicode arrows available, and not provide ones that nobody would use. I expect that this will vary from speciality to speciality, but I'd really appreciate some feedback.
I'm limited to what is in Unicode. (If you are on a Mac, you can bring up the Emoji and Symbols palette and look at the Arrows category)