The 22 mm, 22.5 mm, and 23 mm sizes of Showbiz token have all beeen confirmed, and are distinct if you have all three to compare. If you just have one token, it can be tricky to tell the size to within 0.5 mm. If squinting at a ruler isn't working for you, there are a couple fairly inexpensive tools that you can get to help.
1) Token Size Gauge - I asked Roger Williams mint about selling me one of these, and they sent me two for free! Each is a metal rectangle with 5 semicircles cut out of the edge. Each semicircle corresponds to one of the 5 most common token sizes (0.800, 0.880, 0.900, 0.984, and 1.000 inch) and if you have a token that fits exactly into a semicircle, you can tell what size the token is. If the token doesn't quite fit, you can't measure the size exactly, but you can still tell what range it is in, and this is good enough to distinguish most tokens.
2) Micrometer - This is a bit more expensive, but I think you can get a decent one for around $20 or so (someone correct me if I'm wrong). These take a little practice to read, but will measure token diameters to the nearest 0.1 mm or better. Can also me used to measure other things, and a useful tool to have around.