*Question E4A04:
How is compensation of an oscilloscope probe performed?*  

*Correct Answer is  A: A square wave is displayed, and the probe is adjusted until the horizontal portions of the displayed wave are as nearly flat as possible*  

### AI Response: (may contain errors)  

To compensate an oscilloscope probe, you need to ensure that the probe accurately represents the signal being measured, especially in terms of frequency response. Here's how it's done:

### Correct Answer: A
- **Explanation**: A square wave is used because it contains a wide range of frequencies, including harmonics. By displaying a square wave on the oscilloscope, you can adjust the probe to ensure that the horizontal portions of the wave are flat. This indicates that the probe is neither under-compensated (which would cause the wave to appear rounded) nor over-compensated (which would cause the wave to have overshoot or ringing).

### Why Other Choices Are Incorrect:
- **Choice B**: Adjusting a probe using a high-frequency sine wave for maximum amplitude does not ensure proper frequency response across a range of frequencies. It might only optimize for that specific frequency.
  
- **Choice C**: Using a frequency standard to adjust for deflection time is related to time base calibration, not probe compensation. This does not address the frequency response of the probe.

- **Choice D**: Adjusting a probe using a DC voltage standard for accurate voltage display is related to vertical gain calibration, not frequency response or probe compensation.

### Key Points:
- **Square Wave**: Ideal for probe compensation because it tests the probe's ability to handle a range of frequencies.
- **Flat Horizontal Portions**: Indicate proper compensation, meaning the probe accurately represents the input signal without distortion.

By ensuring the horizontal portions of the square wave are flat, you confirm that the probe is properly compensated and will accurately measure signals across its intended frequency range.