Many people who tested our CES Wireless VR demo asked our how we measured latency.
We used the Leo Bodnar Electronics Lag Tester. The product generates a test patern output via HDMI. The unit is then held up to the display and uses a photo sensor to measure the latency. The measured latency is then output as a number on the display. You can order the product for around $100 directly from Leo Bodnar in the UK.