Close-up of the wheel controls on a J.L. Fisher "Model 10" <a href="//commons.wikimedia.org/wiki/Camera_dolly" title="Camera dolly">camera dolly</a>. "Crab" mode makes the wheels all rotate at the same angle, allowing the dolly to roll diagonally or sideways. "Rear" mode locks the front wheels, allowing the rear wheels to rotate in order to steer the dolly. "Round" mode makes the wheels rotate outward, allowing the dolly to spin in place. It's really cool, trust me.
<a href="//commons.wikimedia.org/wiki/User:Fadookie" title="User:Fadookie">Eliot Lash</a>
CC BY 2.5
<span class="int-own-work" lang="en">Own work</span>