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
"It ain't so much the things we don't know that get us in trouble. It's the things we know that ain't so." -- Artemus Ward aka Charles Farrar Brown