Electromagnetic interference (EMI) is a disturbance caused by an electromagnetic field which impedes the proper performance of an electrical device.  EMI can come from man-made or natural sources such as the sun or the Earth’s magnetic fields. But most of the EMI which causes trouble for precision research applications is caused by stray magnetic or electrical fields generated by machinery or electrical equipment.

Thermal fluctuation is change in temperature in a given environment over time. The primary cause of these changes is natural temperature variation throughout the day, although there are man-made heat sources as well.