Burt,
You do need to calibrate those adapters the first time you use them. Connect a DVM to the output and the power supply to the input.
1. Hold down the left button and apply power. The display will flash on and off.
2. Using the up/down buttons adjust the voltage to read as close as possible to 5 volts. The steps are about 40mV, so get as close as possible.
3. Disconnect power. This saves the calibration.
After doing this, the voltage readout will be fairly accurate.
You do need to calibrate those adapters the first time you use them. Connect a DVM to the output and the power supply to the input.
1. Hold down the left button and apply power. The display will flash on and off.
2. Using the up/down buttons adjust the voltage to read as close as possible to 5 volts. The steps are about 40mV, so get as close as possible.
3. Disconnect power. This saves the calibration.
After doing this, the voltage readout will be fairly accurate.