Mouse:
DPI:
Windows Sensitivity:
In-Game Sensitivity:
zoom_sensitivity_ratio:
True Sensitivity = DPI x Windows Multiplier x In-Game Sensitivity
True Sensitivity (zoomed) = True Sensitivity x zoom_sensitivity_ratio
zoom_sensitivity_ratio
For example, In your launch options add +zoom_sensitivity_ratio 1.0 for zoomed weapons. Default zoom_sensitivity_ratio is 1.2. That means while scoped-in your crosshair will move 1.2 times faster than normal.
One of the best AWPers in the world, Markeloff used zoom_sensitivity_ratio .98
Markeloff CSDM 2012 - Link: https://www.youtube.com/watch?v=RRS5BF5bdLY" onclick="window.open(this.href);return false;
You might be wondering if a zoom_sensitivity_ratio that differs by .02 makes a difference and let me tell you, it does!
400 DPI x 2.80 x .84 = 940.8 true sensitivity
400 DPI x 2.80 x .82 = 918.4 true sensitivity.
That's a 21.6 value difference! To me, .82 feels sluggish while at .84 zoom sens I'm hitting all my flickshots.
Windows Multiplier:
1/11 = 0.0625
2/11 = 0.0125
3/11 = 0.25
4/11 = 0.5
5/11 = 0.75
6/11 = 1.0 (Default)
7/11 = 1.5
8/11 = 2.0
9/11 = 2.5
10/11 = 3.0
11/11 = 3.5
Best to leave your Windows Sensitivity at default 6/11 (middle notch) for a Windows Multiplier of 1.0. There may be problems with pixel skipping at 5/11 for example.
Interesting Read!
CS 1.6 Pro Player Sensitivity:
Link: https://docs.google.com/spreadsheets/d/ ... utput=html" onclick="window.open(this.href);return false;
Ending Thoughts:
In the end, there is no "right" sensitivity. Pick what feels natural to you!
I'll go first!

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Mouse: Razer Abyssus 2014
DPI: 400
Windows Sensitivity: 6/11
In-Game Sensitivity: 2.80
zoom_sensitivity_ratio: .84
True Sensitivity = DPI x Windows Multiplier x In-Game Sensitivity
True Sensitivity = 400 x 1.0 x 2.80 = 1120
True Sensitivity (zoomed) = 1120 x .84 = 940.8