Lathe alignment is one of those things that gets tossed around and there are lots of opinions as to the best way to accomplish it.
So I will toss my opinion into the mix.
You can buy expensive test bars, but they are a waste of money imo. The result will only be as good as the test bar, and good ones are freakishly expensive. For simple alignment, they are expensive toys. I can see their use in a large shop where someone periodically checks the machines, or when a machine needs to be certified. Likewise, they are invaluable to a rebuilder.
For aligning the headstock, I prefer to make test cuts on a piece of stock. I use a 3" aluminum tube about 10" long in the 4jaw chuck. It is important that you use a sharp tool, and that you are using stick that will not sag - so aluminum tube is good for this.
In my (mostly worthless) opinion, this method is far superior to the Rollie Dad Method. Rollie Dad works fairly well on a mill, but it does not take into account the sag of the stock on the lathe, and it assumes the material is not bent in two planes.
Here is Abom doing this method on a big piece of steel on his Monarch
For aligning the tail stock, I prefer the "2 ring method."
For some reason, mrpete makes a tool from steel and aluminum, which is a waste of time. Just use a piece of free machining stock 1" or bigger and machine a valley between the rings. In fact you do not really need the rings, they just let you do the test with less machining.
If you go to Suburban Tools and buy yourself a very very expensive test bar that is guaranteed to some ridiculous degree, it will have been ground on a machine that is aligned by grinding and checking for taper.
