From the specification linked in the article:

> The normalized pressure of the pointer input in the range of [0,1], where 0 and 1 represent the minimum and maximum pressure the hardware is capable of detecting, respectively. For hardware that does not support pressure, including but not limited to mouse, the value MUST be 0.5 when in the active buttons state and 0 otherwise.

What kind of non-sense is this? It's like saying 0 is white and 1 is black, but when a grayscale is not available, 0.5 is black.