There is a fairly decent explanation in the manual.
I use the oprimode on the phantom menace region2 ( as I only ever use dscaler for pal material). The autocalibration will set the capture settings for the card ( the video settings in the menu). Ideally once set you leave the video settings alone and adjust the image for using the overlay settings. (turn full luma range on in the advanced video flags)
I do it this way. Use the scoped settings for TT for my hardware and driver set. Setup the projector settings. ( I then bumped the gamma way down on the overlay and then I did a little touching up on the projector settings ; for the ae100). Now happy my projector is calibrated for the HTPC usign TT. Then I run the dscaler autocalibration using TPM region2 optimode pattern ( from my stand alone dvd player through an RGB to s-video convertor). Once this is done I adjust the Dscaler overlay controls using the optimode patterns ( they are a bit crap but I didn't want to throw NTSC using avia or VE into the mix just yet). The projector settings stay the same as for TT use.
This way I can happily switch back and forth between TT and dscaler and know both are as correct as they can be.