Here is an instrument you do not see every day. A magnetometer, the voodoo is in the fluxgate sensor. But that is nothing more as a boring grey piece of potted tubing. The principle is not so difficult but building a good sensor is. (so I’m told) The 3rd part is software to analyse the data.
The real magic comes from the man who uses this instrument to measure magnetic fields in X,Y,Z directions on places where they have, or want to install, a scanning electron microscope. Those magnetic fields can influence the beam of electrons in the SEM. Interpreting of the data is complex and not many people do this.
The owner was in Norway when it died and he contacted me. He brought it to me the next day and collected it the next day on his way to Germany. It was not a very complex repair. I also placed a new battery the owner already had. The old one bulged and was almost penetrated by the pins from the components because it is mounted under the pcb. It had a low battery beeper but the owner did not hear that so I mounted a bright blue led that lights up when the beeper goes on.