Liquid milk is transferred between a farm tank (10) and a milk collection tanker (11). A control computer (12) is mounted on the tanker (11) and an associated electronic dipstick (14), especially a pressure transducer or an ultrasonic transducer (30) is mounted in the farm tank (10). The level of liquid in the farm tank (10) is determined by the transducer and recorded. Samples may be taken during transfer in accordance with time, weight or volume transferred. In the case of a pressure transducer the readings are corrected to take account of aeration. In the case of an ultrasonic transducer (30) the unit is calibrated to take account of differences in the density of air above the liquid in the farm tank (10).
