The meter reads OL, or the scope trace is flat

What to check, in order, when an instrument is not telling you what you expected.

Both instruments are wired into the circuit like any other part, so almost every surprise is the wiring or the range rather than the engine. Work down the list.

The meter shows ----

The simulation is not running. The digits go blank when there is nothing to measure; press Run.

If it is running and the display is still blank for more than half a second, the meter has not published a reading yet: it integrates over a quarter of a second before it shows anything, the way a real one does, so the first reading lands 250 ms after the circuit starts.

The meter reads OL

On the ohms and continuity ranges, OL means over range: more than 1 Mohm between the leads, which includes the leads being in the air.

The three things that cause it when you did not expect it:

• The black lead is not on COM. Every measurement uses COM and one of the other two jacks. On the volts and ohms ranges the red lead goes in V; on the current ranges it goes in A. The face dims the jack the red lead does not belong in for the position the dial is on.
• The circuit is still powered. The ohms range works by pushing its own 30 µA through whatever is between the leads. Anything else driving that node fights it, and the meter says OL rather than inventing a number. Stop the simulation, or take the supply part off, and try again.
• It really is over a megohm. Two things that are not connected read OL, which is the point of continuity mode.

The meter reads zero, or a third of what you expected

Check what the dial is on. A DC range averages over its quarter-second aperture, so on a square wave it reads the duty cycle times the height. A signal that is high a third of the time really does average a third of its height, and that is the right answer, not a fault. An AC range reads the true RMS of the moving part and ignores the DC offset entirely, so a 5 V rail with no ripple on it reads 0.000 V on V~ and 5.000 V on V=.

On a current range, remember the meter has to be in the circuit, not across it: break the connection and put A on one side and COM on the other. A current meter clipped across a node like a voltmeter reads the current through its own 1 ohm shunt, which is either nothing or a short.

Above about a kilohertz an AC reading drifts low, because the meter samples at 4 kHz. That is a real bandwidth limit rather than a bug, and the scope is the instrument for anything faster.

The scope screen is empty

• GND is not on the circuit's ground. Both channels are measured against the ground clip; with it unclipped there is nothing to measure against and the trace is a gap rather than a line.
• Nothing has been sampled yet. The scope fills the screen in one time base, so at 10 s a division there is a whole minute of waiting before the screen is full. The trace grows from the left while it fills.
• The volts per division is too coarse. A 50 mV signal on a 5 V per division screen is half a pixel. Press - under the volts on the right of the face until it opens up; the circuit keeps running while you do.

The trace crawls sideways instead of standing still

The scope triggers on channel 1 rising through the middle of its own swing, and it says TRIG in the corner of the screen when it has found an edge to do that on. If TRIG is not there, it is free-running, and what you are watching is the newest screen rather than an aligned one.

Usually that means channel 1 is on a node that is not the repeating one. The trigger only ever looks at channel 1, so put the clock, the output or the drive signal there and the thing you are studying on channel 2. A trace with no real swing on it (a flat DC level) never triggers, which is correct.

The generator's amplitude is half what it should be

It drives through 50 ohms, exactly as the box on a real bench does, and that 50 ohms is in series with whatever you have hung on it. Into a 50 ohm load you get half the amplitude you asked for; into a 1 k load about 95% of it; into a megohm, all of it. The figure is printed beside the output posts.

If you want an ideal source with no output impedance, use the plain signal source part instead: same waveforms, no 50 ohms, no knobs.