A computer-based apparatus, including: a memory element storing computer readable instructions; a processor; and a source element to expel a first plurality of drops of a substance with a known density through a medium, and under a set of conditions. The processor executes the computer readable instructions to calculate uncalibrated volumes for the first plurality of drops using respective images of drops in the first plurality of drops. The source element expels a second plurality of drops of the first substance through the medium, and under the first conditions. The processor executes the computer readable instructions to: calculate, using a weight for the second plurality of drops and the known density, actual volumes for the second plurality of drops; and generate, using uncalibrated volumes and the actual volumes, an equation to modify the uncalibrated volumes to match the actual volumes.