Mouse pointer speed

hi
when i set the systems' mouse pointer speed by calling SystemParameterInfo with SPI_SETMOUSESPEED msg, what am i really doing? i mean, for example if i set the mouse speed to 1 (pvParam=1), what pixel distance the mouse pointer gonna move for a single mouse 'tick'?
thx.

Test it?

i tried to count pixels of a mouse tick with the info panel of Abode Photoshop, but it seems difficult to get a accurate value. how would you do it please?