20170215, updated 20220325

MADAR I & II used a magnet variometer to detect UFOs. The MADAR-III DataProbe uses a magnetometer to do this, but also collects data on compass deviations and changes in accelerometer measurements. The original MADAR-I & II were a one-site operation at Mt. Vernon, Indiana. MADAR-III is a collection of a hundred and forty-plus DataProbes located in the United States and about a dozen sites in foreign countries.

In June of 1960 NICAP originally listed 81 primary E-M cases. NICAP published "The UFO Evidence" in 1964 and listed 25 additional incidents.
E-M_Effects_Associated_With_UFOs-NICAP-1960.pdf

Researcher Eric Herr concentrated his efforts toward compass needle incidents. Working together we located over a hundred and fifty incidents. Using that list we were able to locate the reports, many in much more detail.
Herr_Incidents.pdf
http://www.nicap.org/detection/compass/

In 1981 Mark Rodeghier (CUFOS) published UFO Reports Involving Vehicle Interference and  listed 441 incidents.
UFO_Reports_Involving_Vehicle Interference(1981_Rodeghier).pdf

Dr. Richard Haines catalogued 185 E-M cases involving aircraft, alone. In this 1992 paper he listed 56.
Fifty Six Aircraft Pilot Sightings Involving E-M Effects

The NICAP team has researched the following E-M cases on the NICAP site.
E-M Cases on the NICAP site

The recordings from the MADAR-III DataProbe are in the form of data sent to one of the MADAR Servers at a rate of one line of data per minute. When triggered by a specific change in the field the device goes into alert mode at a rate 60 times faster until the alert is over.