Larry, It's "nominal 230V". Depending on utility, your voltage could range from 110V to 120V per hot leg. That gives you 220V - 240V when they are combined into a welding receptacle. Your welder won't care.
If you have 208V, then you may have to make a change in your machine.
Don't sweat the 10V. Go to an electrical supply and get a NEMA6-50 receptacle and wire it just like an old dryer circuit (2 hots + ground).
I'm getting by now with an extension cord that plugs into my dryer outlet and has a NEMA6-50 box on the other end of 30' of 10/2 cord. This works fine for my 175 amp MIG box.