Imagine a 3-axis joystick that can also sense translation. So aside from pitch/roll/yaw you also get the linear up-down/left-rigth/forward-back axises.
I can see how pitch roll yaw would work, but I can't imagine how linear movements are made on the same joystick? Maybe up and down is push and pull but what about the other directions? Do you push the device itself?
The trick in comparing it to a joystick is that it can distinguish between tilting the control to a side, and pushing the control to the side. Does that help? Similarly, it can detect pushing straight down and pulling straight up.
Looks like current incarnation is Stewart platform lookalike optical setup for all axes[1]. I misspoke in a different comment: Mine was older SpaceBall 5000 model, and it was more like two joysticks joined at the stem.
