How to decrease trackpad tracking speed on demand? I'm using separate magic trackpad and (still, but that's not a requirement) Mac OS 10.9.5. I'm looking for some convenient and free way to decrease tracking speed on demand, for example via additional gesture or a keystroke. 

I'm a developer, so, quite often I need to precisely move cursor one-two pixels aside while inspecting layouts, picking colors, moving panels here there and currently with magic trackpad that's terrible. 

One of good options I'm looking looks like this: scrolling while holding a key produces slow and precise mouse pointer movement.

Tried to search, but not very successfully:


MagicPrefs: nothing like that, but, seems some plugin may achieve that.
SmoothMouse: nope.
SteerMouse: paid, does not support Apple Magic Trackpad.
ControllerMate: paid, looks like this is what I need, but I didn't manage to achieve what I want (too much time spent).
iMouseFix: nope.


As an option I could make some script up and bind it to the keys, which will change tracking speed or an entire app, but I'm not sure about that and consider that as a last resort. Don't like additional mouse option for precise movements, also I rarely use macbook's built-in trackpad, so I need something universal.
BetterTouchTool is the free tool of your choice:

With a simple modifier key you may decrease or increase tracking speed temporarily after configuring the different speeds:



To toggle cursor speed, create a new gesture (optional with a modifier key) or a keyboard shortcut (no screenshot here - just choose the keyboard menu instead of the trackpad menu) and choose the predefined action -> Other Mouse Actions -> Toggle Mouse Speed. 



I don't own a Magic Trackpad but this works at least with my MacBook Pro trackpad.