There's supposedly some "alternative" way to make it zoom in/out by holding and then moving up/down, but I can't get it to work.
To zoom with one hand, do a double-tap, and upon the second tap, hold. Then slide down to zoom in and up to zoom out.
i.e. tap, tap+hold... (while holding) slide up/down
You can tune a piano, but you can't tuna fish. You can tune a filesystem, but you can't tuna fish. -- from the tunefs(8) man page