The PDX10/950 operates over the aperture scale at 0db (no -3db setting possible but not necessary because of its low noise profile). The scale has 24 x 3db clicks with f4 as the centerpoint. In manual mode the exposure bar will start at f4.0 and with each (wheel-) click, exposure will increase +3db ( half stop) or decrease -3 db half stop). After max aperture f1.6 the gain clicks are in 3db (half stop) increments. so from the center at f4 going to the right we have:

Aperture +3db	Gain +3db
f4.0, f3.5, f2.8, f2.4, f2.0, f1.6(0)	f1.6(+3db), f1.6(+6db), f1.6(+9db), f1.6(+12db), f1.6(+15db), f1.6(+18db)
f4.0 is the center of the scale
center	lower light

(Lens in widest mode.)

The shutter speed is independent of the aperture except when the auto shutter is 'on'. Normally in the AE mode the camera will hold 1/50th and keep closing the aperture until about f6.9 at which point it will start upping the speed to compensate for brighter conditions. If you lock the auto shutter 'off' then the camera will choose apertures smaller than f6.9.