How to get rid of different mouse tracking speeds on dual screen setups

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I am using a MacBook Air 11 "2011 Model with Mac OS X Lion hooked up with a Cinema Display 27" and I get two different mouse tracking speeds (I am using a Apple Magic Mouse) when I move between the two screens in a two screen setup.

I have to move the mouse 20cm to move the cursor from screen to the other.

However, I have to move the mouse 40cm to move the cursor from one end of the 11 "screen to the other!

I can only adjust the mouse tracking speed, make it faster on the 11 "screen, but it makes it too fast on the 27" screen ...

Anyway I can fix this? This issue did not occur when I was running a MacBook Pro 13 "when Snow Leopard and the same 27" screen.