pet2000:
DPI changes the accuracy of the cursor on the corresponding resolution display.
Uh?
Put simply different DPI changes the speed of the cursor at 1600dpi it will move 1600 pixels (dots) on the screen per inch of movement while at 800dpi it will move only 800 pixels per inch.
If you're after accuracy then it's better to get a mouse with one of it's DPI that fits the speed you want rather than changing the speed settings in your operating system because it's the mouse that does the processing and tells how many pixels should be used, so all the operating system can do is multiply this. e.g. if you triple the speed the minimum amount of pixels you can move is three as each single pixel movement the mouse says should happen has to be changed to a movement of three pixels by the operating system.