Issues relating to each element in the determination of a tank's contents are examined: level/density measurement, calibration, and its reverification. Systematic errors associated with dip tube pressures that are measured to derive level/density are investigated, experimentally. The conversion from these pressures to level/density is then addressed, and the simplest form is found to be adequate. A revised regression model is proposed to obtain a calibration from biased calibration data from one or more calibration- runs. Severely biased calibration data can be eliminated, reducing the calibration error due to biases to a minimum. It is shown that a more accurate representation can be obtained using cubic splines. Finally, reverification issues are addressed by proposing a new continuous fill approach.