This is very important, because a unicycle wheel with any offset will tend to pull to one side. When I rebuilt my first 36’er wheel, I experimented with wheel dishing to counteract the typical road camber I see here in LA… and discovered that a 2mm dish to the right did a very good job of that. Of course, if you’re a Brit, then that would be a dish to the left
Okay then… here’s something I call the “poor mans dishing tool”. If you’ve seen a dishing tool before and tried to buy one, you already know that they are quite expensive if you’re going to only use them for those rare moments that you’re working on your own wheel. Besides, in my case, I discovered that nobody makes one that is compatible with a 36" wheel!
So… 4-6 rubber bands, a couple of sticks a few inches long (any kind) and a STRAIGHT piece of wood as long or longer than your wheel diameter.
Use the rubber bands to wind around and hold the two sticks at right angles to the straight piece of wood, about where the rim should be. You now have one long piece of wood with a couple of adjustable short sticks.
Lay the straight piece of wood against a good point of reference, your bearing or the end of your crank/hub axle, and adjust the positions of the two sticks until they just BARELY touch the rim on both sides. Make sure that you have three points of contact… the rim on each side plus your point of reference.
Now lift the wood away and flip the wheel over, lay the piece of wood against the same point of reference on this side and see if it matches. You will be able to clearly tell which way the rim should move, which is the side that you want to tighten towards (and loosen the other side).
RE-do this dishing test as needed till you get the wheel centered.
Having build probably 1,000 wheelsets in my bike shop days, this is the way I do it now The quality of the result is far more important than the cost of the tool.
Oh, and one other point… if you leave the wheel in the frame but remove the cranks, you can use the end of the crank/hub axle as your point of reference while still keeping your wheel in it’s natural truing stand.