Earth's surrounding geomagnetic field features the same magnetic properties as magnets. The shape of the field is not fixed but changes regularly. However, due to external factors (solar wind, CME, etc.), additional geomagnetic disturbances sometimes occur. K-index uses the logarithmic scale to display the variation levels in the geomagnetic field over specific regions. The values range from 0 to 9 at 3-hour intervals with 0 being quiet and 9 indicative of radical change. The algorithm that determines K-index varies depending on the measurement for undisturbed daily variation of solar radiation (solar quiet curve, Sq curve). In order to calculate the K-index, KSWC uses the FMI algorithm identical to that of NOAA’s SWPC, in cooperation with the center. The algorithm derives the Sq curve by using real-time observed data and horizontal components of geomagnetic data from the previous day to the next day comprising a 24-hour period. This method enables the calculation of the K-index, which is represented by the logarithmic scale based on the level of variation of geomagnetic activity as measured by subtracting the Sq curve from the real-time geomagnetic data of horizontal components (H and D).