Valve's first efforts at motion tracking involved putting QR code-like tags all over a room's walls; a camera on the headset read the codes, got a precise location, and moved the wearer accordingly.
Valve's early headsets were noted for having very low latency, compared to the relatively blurry Oculus Rift. This is a small, one-eye prototype.
This was Valve's "first glimpse of presence," and it's the headset that got a lot of people talking about VR when Valve showed it off at Steam Dev Days in 2014.
This version of Valve's headset appeared in public a few months later, in mid-2014. Instead of having a head-mounted camera track barcodes, an external camera tracked dots on the headset, more like the Oculus Rift.
Like the Vive, the dot-tracked headset came with a controller that was also covered in motion-tracking dots.
After the dots, Valve moved to its current laser-tracked system. "Our first approach to this was to just hot-glue the sensors to one of our dot-tracked headsets," reads the placard.
Another step towards the Vive, this one with integrated sensors.
And now we're almost up to the present, with the prototype controllers that accompany Valve's Vive demo.