Incorrect in original (sometimes):
CT arrow pointing toward load → causes negative power.

Corrected:

Hold the "SET" button for 5 seconds while powering up. The display will show F x.x (e.g., F 2.0 or F 2.1).

There is typically one main button (or touch area) on the front.

To Reset Energy (kWh):

To Set the Power Alarm (if supported/enabled): This is where the "patched" version shines.

If you are using this with Home Assistant or ESPHome, the PZEM-051 (patched) is excellent because it is less prone to disconnection loops.

Example ESPHome Config Snippet:

uart:
  rx_pin: GPIO3
  tx_pin: GPIO1
  baud_rate: 9600
sensor:
  - platform: pzemac
    current:
      name: "PZEM Current"
    voltage:
      name: "PZEM Voltage"
    power:
      name: "PZEM Power"
    energy:
      name: "PZEM Energy"
    update_interval: 10s