The K-index scale summarises geomagnetic activity at an observatory by assigning a code, an integer in the range 0 to 9 (0 being the least active field and 9 the most active field) to each 3-hour Universal Time (UT) interval. K-Indices are available for Lerwick, Eskdalemuir, Greenwich, Abinger and Hartland Magnetic Observatories. From 1954-90 the values are hand scaled, from 1991 to the present day they are automatically scaled. The data not only aids scientific research into rates of change of the magnetic field and increases the accuracy of the BGS Global Geomagnetic Model, but also provides data to exploration geophysicists engaged in current and future oil exploration.