How to find sx and sy and F intrinsix matrix in camera calibration

I would like to ask about my problem. I has been doing measurement about camera calibration and i have problem how to find sx and sy value ? sx and sy value will i do to find F (Focal length) in world units. i has searched in parameter camera but i didn't found it. this is i'm doing for to know the effect of variations of the camera-object distance with focal length. please help me, thanks so much.

"The coordinates [cx cy] represent the optical center (the principal point), in pixels. When the x and y axis are exactly perpendicular, the skew parameter, s, equals 0.

fx = F*sx fy = F*sy F, is the focal length in world units, typically expressed in millimeters. [sx, sy] are the number of pixels per world unit in the x and y direction respectively. fx and fy are expressed in pixels."