Hi Geoff,
I found this:
https://www.quora.com/What-is-the-DP...-do-you-use-it
Quote:
"DPI stands for "Dots Per Inch". The measurement being linear. In short, this is the speed of which the mouse moves on your screen in relation to you physically moving the mouse. Most mice move roughly about 800DPI by default. This is considered the standard speed of any mouse. Now that's to say if you physically move the mouse 1 linear inch, the mouse on screen will move roughly 800 dots in length.
Increasing the DPI means that same inch you physically moved the mouse equates to more distance on screen. And of course decreasing the DPI results in less distance traveled on screen.
If a mouse has a DPI button, it typically means you can change the speed of the mouse's on-screen movements on the fly by simply pressing the button. Most mice that have dedicated DPI buttons have preset DPI configurations. Often software will allow you to modify the DPI presets as you, the user, wishes. But most mice that have dedicated DPI buttons will often come preset with 3 speeds; Slow, standard, fast. Exactly what these DPI measurements are will vary from manufacture to manufacture, but if you press the DPI button then move the mouse, you should instantly see a chance in your physical mouse movements and the distance the mouse travels on screen based on those same moments.
You'll often see gamers going through DPI settings more than any other users, though graphic artists tend to use it as well to help make fine selections and changes."
END QUOTE
Rgds.
Dave