Which one of the following instruments should be used at

Which one of the following instruments should be used at Min the given figur e for the measurement of magnitude as well as direction of the displacement?

1. Permanent magnet moving coil voltmeter
2. Vacuum Tube voltmeter (VTVM)
3. Transistor voltmeter (TVM)
4. Phase Sensitive Detector (PSD).

M should be able to detect phase reversal if not strictly phase sensitive. Phase sensitive detector can well serve the purpose.