0.793471, regardless of aspect ratio.

It does vary with fov_desired. Use the following formula to calculate it for any value of fov_desired:

(tan (<scoped FOV> / 2) * <fov_desired>) / (tan (<fov_desired> / 2) * <scoped FOV>)

I feel that I should point out that there is no "correct" value, and you should use what you feel comfortable with, but the value given by the above formula should feel the closest to your unscoped sensitivity.

Edit: scoped FOV is 20 degrees for the sniper rifle.
Edit 2: switched "unscoped FOV" to "fov_desired" in formula for clarity.

Aspect ratio doesn't change the value, it's based entirely on the fov_desired value (which is 90 for almost everyone).

zoom_sensitivity_ratio 0.793471413188092380619906740908785437547348780566443970924

e: ninja'd

zoom_sensitivity_ratio 1.0 is accurate for fast flicks to the very edge of your screen on 4:3 (or the imaginary borders of a 4:3 screen for higher aspect ratios). 0.79347... is accurate for movements that approach no distance. Because you'll probably be doing more of that and adjusting your movements rather than closing your eyes and doing giant flicks, 0.79347... is usually better to have if you're not already used to something else as sniper.

thank you, i was under the impression that the lesser fov would lead to a different zoom_sens value