Equipment requirement:-

• 0.0V and 2.0V voltage Reference sources (preferably switchable)
• 5K Lin potentiometer (wired in series with a 1K5 resistor and Reference output as per Figure A)

Figure A

Either:-

• Method 1 - a high-accuracy frequency meter, or
• Method 2 - an accurate audible tone generator and a small mono amplifier with a 2-input mixer
  

Power the ES20 on and let it warmup for several minutes before starting the calibration process