How do I check my dryer (voltage) receptacle with a Sperry DM-210 without killing myself?

I bought a digital voltage reader last night at Home Depot. A tenant called me yesterday and said, " Mike, my dryer runs but does not get hot. I think you should check the voltage." Its a 220v receptable and I need to know how to turn on my reader, plug the probes in (black on left, red on right, turn device to 600 and stick each probe in both slotted legs? Any advice can help please.