1. A method for measuring the quantity of fluid in a tank comprising the steps of: simulating a plurality of sets of electromagnetic eigenfrequencies of the tank for a range of fill levels using an electromagnetic eigenmode solver algorithm, wherein each simulated set of electromagnetic eigenfrequencies represents a specific fill level within the tank; inputting the simulated plurality of sets of electromagnetic eigenfrequencies into a computer database; transmitting a first range of radio waves using a transmitting device located inside the tank; receiving the first range of radio waves using a receiving device located inside the tank; identifying a measured set of electromagnetic eigenfrequencies in the first range of radio waves using an eigenfrequency identifier algorithm; comparing the measured set of electromagnetic eigenfrequencies to the simulated plurality of sets of electromagnetic eigenfrequencies; selecting a match between the measured set of electromagnetic eigenfrequencies and the simulated plurality of sets of electromagnetic eigenfrequencies using a matching algorithm, wherein the match is one simulated set of electromagnetic eigenfrequencies from the simulated plurality of sets of electromagnetic eigenfrequencies; determining the fill level of the tank based upon the match.