SoUnits(3) on Linux
The text 14bf5c3bf498, as Debian 7 (Wheezy) shipped it.
The SoUnits class is a node for setting unit types. Even though Coin doesn't care what units you are using in your scene graph per se, there's an advantage to using SoUnits nodes: you have a way to split your scene graph into different 'conceptual' parts.