Hello jj,
This button can be used to turn on/off backlight and reset energy reading.
Reset energy reading:
Step 1: Keep pressing the button for 5 seconds until the energy reading flicker, then release button;
Step 2: Short press button, the energy data will reset.
Step 3: If you don’t want to reset it, please keep pressing button again for 5 seconds until the energy reading doesn’t flicker.
Best regards.