NV magnetometry makes use of atomic defects in diamond, called NV centres, to measure magnetic fields. The extreme sensitivity of NV centres to their surrounding magnetic field is readily observed in their radio-frequency spectrum, using a technique known as optically detected magnetic resonance (ODMR) spectroscopy. A key advantage of NV magnetometry is that NV centres have a well predicted and reproducible behaviour, which provide unambiguous information on the strength and direction of the magnetic field.