What exactly am I trying to do when I set the zero offset? Do the numbers need to match? Does the actual number matter?

Don't worry about the actual number. The purpose of the zero offset is to measure the base level of stress on the internal strain gauges of the PowerMeter before you apply any pressure to the pedals. It will change with temperature, pressure, impact, and this is normal, the SRM system just needs to know what it is to give you accurate power data.
When you go into zero offset mode, the top number is the actual number, the base value right now -- watch for it to stabilize, and then hit the "Set" button.
The bottom number is the stored number from your last ride, and is no longer relevant.
Once you hit set, the top number will be stored and they will match.

The power reading is too low or too high

Once you've been training with power feedback for a short while, you'll have a pretty good feel for what power you normally produce. If you notice that the power being shown on the PowerControl is too low or too high, there are a few things you can check.

Please check that the zero offset is correct.

For PowerControl V users:

1. check that you have the correct slope entered into your PowerControl. Press the "Mode", "Pro", and "Set" buttons all at the same time. This takes you into the first setup screen. Press "Mode" six times to get to the second setup screen. The slope that the PowerControl is using for it's power calculations is shown at the bottom left of the screen (e.g. "25.0").  If it isn't the correct slope for your PowerMeter, press the "Mode" button once more so that the "S" in the bottom right of the screen is flashing. Then correct the slope by pressing the "Pro" button to increase it or the "Set" button to decrease it. Press and hold the "Mode" button to exit the setup screen when you're finished.
2. check that the zero offset is correct.
3. check that the sensor cable is positioned correctly, so that it is receiving data from the PowerMeter through the whole 360° revolution.

If you've done all of the checks listed above and the power reading is still too low, you can send it in to an SRM Service Centre for calibration.

Can I view my Average Power or Normalized Power while riding?

SRM does not calculate Normalized Power. This is a term calculated and trademarked by Training Peaks (www.trainingpeaks.com).

Your SRM does calculate Average Power, Heart Rate, Speed and Cadence. You can view this while riding:

• Hit the Mode Button and you can see the average display mode for 20 seconds.

If you have a PCVI:

• Connect your PowerControl to your computer
• Open SRM WIN
• Go to PowerControl Set up
• Click on Special
• You will see a Return to Main Screen with the choices of Automatic or Manual.
• Select Manual.
• When you are riding and you click your Mode Button to see the Average Display - it will stay in this average display mode until you manually exit it by hitting the mode button again.