Precision and Accuracy
A machine is accurate when it does exactly what you want and it is precise when it does exactly what you want over and over again. I am going to talk about CNC (computer numeric control) plasma cutters here because with hand held plasma cutting equipment it is your skill and talent that determines precision and accuracy. With a machine, it is a variety of factors that do not included skill or talent.
Generally, mechanical machining processes lend themselves to easily assign standard tolerance, but that is not so for Plasma Cutting equipment. The actual machine (the cutting table, motors, rails, CNC, and bridge) actually have tolerances that far exceed the tolerances of the plasma cutting process itself. There are many different factors that can influence the precision and accuracy, collectively referred to as the quality, of the plasma cut including: the unit's power settings, the type of consumables, the gases used, type of material, characteristics of the material being cut, gauge (thickness) of the material, the layout of the parts on the plate.
Other factors affecting the cut quality include construction and condition of the rail system, the type of CNC unit and PC used, the sizing of the motors relative to the gear box, the drive systems used, etc. As you can see there are lots of details that can affect the cutting quality of plasma cutting system. So when you are buying a CNC plasma cutter it is best to ask the manufacturer to provide you with cut samples made using the machine and plasma cutter combination that you are interested in. Ask that the samples closely resemble what you will be cutting with the machine. That way you will have an idea of the quality of the cut with different set ups. If the quality is not up to snuff then keep looking. You will be dropping a pretty penny on plasma cutting equipment, so make sure it does exactly what you need with accuracy and precision.