A pair of precision coils and 400 turns of wire are wound on a heat resistant former of about 150 mm diameter. The coil is comprised of a support rod, which fits on the holders of the track system supplied, which enables them to be aligned on a common axis for measurements and study of the magnetic fields. Normally used in pairs, each coil has 4mm terminals and their distance apart is adjusted over the track supplied. The maximum current in the coil is 1A to avoid overheating. Direction of current is marked on each coil.