If you are talking about an impeller-type dishwasher, they used a metering coil to determine the amount of water in the dishwasher by measuring the amount of energy the motor drew to overcome the resistance of the water to the motion of the impeller. Each fill is 6 quarts of water. If you can measure what drains out, you can determine if it is overfilling. The metering coil is a little cylinder-shaped thing. It is adjustable with a screwdriver, I believe.
Also, make sure that the strainer around the impeller is mounted so that the fine holes are at the top and the large holes are at the bottom. Some owners said that silver basket needed to be in the left front of the rack and a pan or bowl in the right front to make sure water did not push past the gasketless door closure and drip out. I do not know if that is true or not.