SoUnits(3) on Linux
The text 5cfc3d5edeb9, as Debian 4.0 (Etch) 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.