Question

What effect could the DMM have when inserted into the circuit in parallel? In series?

Answer 1

DigitalMultiMeter (DMM) is used to mesaure volatges and currents in an electrical circuit.

Generally, when DMM is used to measure voltage across two points, it is connected in parallel. At this time it offers high resistance so that there will be no loading,i.e. it doesn't effect the circuit..

Similarly when it is used to measure current in a branch, it is connected in series. At this time it offers low resistance so that the brach resistance will be as same as original branch resistance. Thus drawing same current.

Otherwise, if DMM in current mode is connected in parallel, Since resistance of ammeter is small, most of the current flows through ammeter(DMM), thus affecting the original circuit.

Similarly if DMM in voltage mode is connected in series; it doesn't make sense since you are measuring no volatge difference.