4 ms, even measured in terms of gray to gray, seems incredible. And as a matter of fact, it is - literally.

We measured the actual latency of the VX924:

Again we'll recall our test method:

The curve shows the different latency values for different levels of gray. A black-white alternation is shown on the curve by a point at X-axis 255, a black-gray alternation produces a point at X-axis 125, a black-dark-gray alternation shows as 50, etc.

The official ISO latency rating specified by the manufacturer is only for black/white transitions (0/255). While the value we measured agrees with the manufacturer on this point, it's not of much value in judging the actual responsiveness of the panel in practice.

As you can see, we don't share AU Optronics' optimism about the AU190EN4 V.5 panel used in this monitor. The fault lies in the obvious lack of standardization of latency measurements. The ISO latency measurement protocol isn't perfect - far from it - but at least it is relatively well defined, with effective protections against exaggeration. With the GTG system, we're getting announced values that have nothing to do with reality most of the time.