In cooperation with Stanford University, Geometrics Inc. has installed and maintains a permanent total-field magnetic field observatory at Stanford's Jasper Ridge Biological Preserve. This observatory location permits measurement of the variation of the magnetic field in a setting that is relatively isolated from man-made electromagnetic signals. These total-field measurements are recorded and archived in several locations including this website. Geometrics archives are available free of charge. Click here. The magnetic field is sampled at rate of 10 Hz and each data file contains a midnight-to-midnight time-stamped record of the magnetic field strength.