A packaging machine with a platform (6) on which a container (27) can be supported and sensor (23) for detecting the presence or absence of a container (27) at a position on the platform (6). A control apparatus with a memory is configured to cause the packaging machine to perform a setup operation in which relative motion between the platform (6) and sensor (23) is caused and monitored. A parameter relating to the amount of relative motion from a starting position to a position at which the sensor output changes to reflect the presence or absence of a container (27) is stored in the memory. The control apparatus is also configured to use the stored parameter to control the machine in a packaging operation.