A mobile printer includes an ultrasound sensor to sense a set of ultrasonically-sensed positional data points of a print nozzle of the printer, at least one optical sensor to sense a set of optically-sensed positional data points of the print nozzle, and a processor. The processor is to apply a correction function on the set of ultrasonically-sensed positional data points and on the set of optically-sensed positional data points to provide a set of corrected positional data points of the print nozzle and is to cause the print nozzle to deposit according to a print request and according to the set of corrected positional data points.