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Dear Aunt TUAW: Help me adjust my mouse tracking on the fly

Dear Aunt TUAW,

I'm happily running Lion on my computer now, but I've noticed an issue with the mouse tracking speed that is driving me batty.

I use a dual-screen setup with my 13" Macbook Air and a 23" Apple Cinema Display (with a Magic Mouse), and the tracking speed doesn't remain constant across the two screens.

Adjusting for a normal tracking speed on the Cinema Display results in painfully slow mouse movement on the MBA -- almost as if the proportional movement (relative to the screen size) is calibrated to remain the same.

Is this an early Lion bug, or is this a new "feature" that I can somehow unwind?

Please help!

Your loving, but annoyed, nephew,
Nate

Dear Nate,

Auntie doesn't have good news for you. And that's because the mouse speed option cannot be set on a per-monitor basis. Mouse tracking is controlled as part of system defaults, in the Universal Access preferences pane.

The actual preference is called mouseDriverMaxSpeed and can range as an integer between 1 (lethargic) and 32 (zippy). Here's how you'd read the current setting from the command line.

defaults read com.apple.universalaccess mouseDriverMaxSpeed

Whatever number you set to feel right on one monitor will either feel draggy or hyper on the other.

Unfortunately, the problem with auto-scaling the mouse lies in detecting when the cursor has changed between screens. There's no system notification generated so nothing for Auntie to build a tool on, to update the defaults as you move the cursor around.

So, Auntie thought she'd throw this one out to all her other nephews and nieces. Have any of you found a solution for Nate that doesn't hinge on system notifications?

Hugs,

Auntie T.