Calibrating Gravity I2C Digital Wattmeter Problem

I've hooked up the Gravity I2C Digital Wattmeter do my Arduino Uno for the purpose of calibrating the unit as per the instructions for unregulated power supply but my Serial Monitor starts with 20mA for the current but goes down to 16mA, then back up again - its variable. Same goes for the multimeter - it varies from 20mA to 18mA or so.

What should I set for these parameters?

// Revise the following two paramters according to actula reading of the INA219 and the multimeter

// for linearly calibration

float ina219Reading_mA = 1000;

float extMeterReading_mA = 1000;