According to the Noob-to-Pro wiki:
“To rotate around a horizontal axis (upward), leaving objects’ horizontal orientation unaltered, use SHIFT+ALT+SCROLL, or using the keyboard, NUM8 and NUM2”
Unfortunately Shift+Alt on the Mac is used to create special characters and therefor this combination doesn’t work (Shift+Ctrl+Scroll for vertical axis rotate works fine). Has anyone figured out a way around this?
Three button mouse with scroll