An infusion pump includes an actuator having an output shaft a pump actuator having a length (lactuator) moved by the output shaft and in contact with tubing, such that the pump actuator at an output shaft actuated distance (x) creates flat contact areas with the tubing, and wherein remaining non-contact areas of the tubing are at least substantially circular in shape and a logic implementer configured to use at least two relationships to solve for a same number of variables to calculate a cross-sectional area of the tubing at an output shaft actuated distance (x).
