The stand SHOULD be centered at the factory, but you can check this. Put in a reasonably good (should be true, doesn't have to be dished exactly) wheel and adjust the arms that indicate the rim. Note the distances on each side. Then flip the wheel and again, note the distances. If they are consistent (that is, you have a 4mm gap on the right, and a 6mm gap on the left, and you get the same 4mmR and 6mmL gaps when you flip the wheel) then the wheel is dished ok. If they are consistent and the distances are the same(e.g. 4mmR and 4mmL), then the wheel is is dished ok, and your TS-2 is centered. If the left and right gaps change when you flip the wheel but are mirror images (4mm L and 6mmR changes to 4mmR and 6mmL) then the wheel is not dished right but your TS-2 is ok. If the gaps are neither consistent nor mirror images, you need to do a little math to center the TM-2.

Or your can spring for the Park centering gauge for truing stands. About 80 bucks. I did, and found out that my centering job had been 1mm off. But you're not supposed to use the TS to get the exact dish.

You should be able to create a dish gage with some pieces of wood (1x2 works) and some all-thread with matching washers and nuts. A long enough piece of wood to span the rim, with spacer blocks glued and/or screwed to the ends to give you spacing. Then you drill a hole in the center and install the all-thread (threaded rod) with washers and nuts. In fact, if you drill your hole a little small, your all-thread will probably form threads when you install it. I scored an old VAR WAG-1 dishing tool for cheap (below).

I recently inherited a wheel my step-dad made. He used his own dishing tool (of the blocks of wood variety), and centered the wheel in a frame. It was spot-on center, true, and had all the spokes with nearly identical tension. You've kind of got the Ford F-150 of truing stands (the Rolls Royce is the DT Swiss model but it costs 2 grand). Your model will give you excellent results for a long time.