what it means for a "source" or "sink" to be floating. What are the consequences of associated devices being floating or non-floating? Is the multimeter floating or not? What about the oscilloscope? What about the power supplies? It is extremely important to understand and keep this in mind when "wiring" sensors and industrial computer systems? For example, is the SSR system floating or not? Distinguish between "computer" and "field side" as well as high power vs low power (signal) circuits.