A method of calculating a volume of a drop pendant using a microprocessor. Included in the method are generating a gravity vector based on a direction of gravity with respect to the drop pendant; establishing a reference frame of the drop pendant for an image processing based on a reference point of the drop pendant and the gravity vector; generating a first reference line associated with the reference frame for representing an actual orientation of the drop pendant; generating a second reference line associated with the reference frame for representing a longitudinal axis of a chamber in which the drop pendant is located; comparing the first and second reference lines with respect to the gravity vector; and calculating the volume of the drop pendant based on the comparison of the first and second reference lines and the gravity vector.