How do I connect an oscilloscope to a power supply or function gen.?
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1.
(a) Your test circuit.
(b) The right way to connect up a 2-channel oscilloscope.
(c) Connecting the ground clips to two different voltages on the circuit will cause current to flow through the earth connection inside the oscilloscope.


  "CAREFUL NOT TO CAUSE A SHORT CIRCUIT".


The risk is that you might try to measure the voltage as shown in Figure 1c and attach the two earth clips. If the circuit is a high current circuit then
a high current will flow through the red lines and possibly burn up the wiring or PCB tracks inside your oscilloscope.

The correct way is to wire as shown in Figure 1b, take two measurements and calculate the voltage across R1 as \$ V_{R1} = V_2 - V_1 \$.