I'm building my first wheel, and have got it laced and on the truing stand. I'm now trying to get the wheel dished correctly. Assuming that the truing stand is perfectly symmetrical, what is the need for a dishing tool? If it is the case that truing stands are not normally symmetrical (ie, the calipers are not perfectly centred to the uprights), then do I just set and check the dish with the special dishing tool, and then only use one arm of the calipers? (ie, the wheel, when correctly dished, will not sit in the centre of the calipers).

Thanks in advance!