| The file is comprised of instantaneous absolute values of the geomagnetic components
D, H, and Z or X, Y, and Z at 1-minute intervals. These values were derived either
from analog recordings (magnetograms) with the aid of semiautomatic digitizing equipment
or from digital recordings made directly on magnetic tape. These data are available
from about 50 observatories operated by the United States, Canada, Australia, Japan,
United Kingdom, Taiwan, Sodankayla, Iceland, Finland and France. |