What units are captured by a Vive Controller ?

What units are being captured by Unreal when I track the physical distance/movement of a Vive Controller ?

Hi I would like to calculate the “physical distance” moved by a vive hand controller during a particular experiment.
I have the following code working but I am unsure what units are being captured by the vive and passed into unreal.
Does anyone know (I checked online and in the forum but no sign of anything related).