The K index was devised by Bartels et al. (1939) to provide an objective
monitoring of irregular geomagnetic activity. The K index was then routinely
used to monitor the magnetic activity at permanent magnetic observatories as
well as at temporary stations. The increasing number of digital and sometimes
unmanned observatories and the creation of INTERMAGNET put the question of
computer production of K at the centre of the debate. Four algorithms were
selected during the Vienna meeting (1991) and endorsed by IAGA for the computer
production of K indices. We used one of them (FMI algorithm) to investigate the
impact of the geomagnetic data sampling interval on computer produced K values
through the comparison of the computer derived K values for the period 2009,
January 1st to 2010, May 31st at the Port-aux-Francais magnetic observatory
using magnetic data series with different sampling rates (the smaller: 1
second; the larger: 1 minute). The impact is investigated on both 3-hour range
values and K indices data series, as a function of the activity level for low
and moderate geomagnetic activity
