That would do the job but it's rather expensive! A modern digital caliper is what I use and mine cost me only £10. Before you rush out and spend on a guage though, check the RF calibration. Focus is pretty certain to be off unless that's right. Use a flat bar across the mount and measure off that.
The other quick check would be to set the lens on infinity, wide open, and shoot something that's quite distant - preferably in the hundreds of meters rather than tens. If that comes out wrong then I'd certainly suspect either the lens or body register. Ideally you need to get both of them right rather than compensating one with the other, otherwise you'll have an issue with other lenses if and when you use them.