The Pentax flash control system lets you set a flash compensation value on the camera body which is cumulative with any value set on the flash itself. Having two independent settings is most important when using multiple flashes for a scene, but it also gives increased flexibility, since it adds a couple of stops to the range and because many Pentax camera bodies can work in ⅓-stop increments.
With the exception of the AF200FG (which only offers Auto, -0.5, or -1), the Pentax flashes allow compensation from -3 to +1 in half-stop increments.
The Sigma EF-530 DG Super and EF-610 DG Super also allow compensation from -3 to +1 in half-stop increments. The Sigma ST models just follow the on-camera setting.
The Metz flashes from the 48 AF-1 up allow EV -3 to EV +3 in third-stop increments; the 44 AF-1 also allows flash EV compensation but I'm not sure what the limits are. The lower-numbered modules have no independent compensation control.
The Promaster and Tumax flashes don't have separate on-flash settings (but are still affected by the camera's setting for flash EV compensation.)
