The motion of individual granular particles has been experimentally observed in a horizontal batch ploughshare mixer. A technique called Positron Emission Particle Tracking has been used to locate a radio tracer particle with time. A quantitative picture has been constructed to determine when a particle moves between inter-plough regions within the mixer. Results are presented for a single case of 12.5% fill (volume basis) of rice where the ploughs rotate at 2 Hz. Particles were found to displace with a regular oscillatory magnitude of 9-14 mm due to the motion of the ploughs. However, larger distances of travel were far less frequent. The position of the particle relative to the blade has been determined when the particle crosses the plane in which the blade rotates. Frequency distributions of the lead or lag angle between the tracer and blade show the influence of adjacent blades and indicate the importance of the axial separation distance and angle between plough blades. The techniques presented here permit characterisation of the internal flows and development of a knowledge of the influence of machine design and operating parameters critical to mixing.