Get current wattage from Meter SML

Hi Guys,

i have a meter that only exports 1.8.0 (import) counter (total increasing) to my home assistant instance. The counter will be read every 2 seconds and the value will be sent via MQTT Sensor Message.

I like to get a delta statistic with extrapolate to get Watts per Hour. So if the Meter raises from 0,000 to 0,002 kWh in 2 seconds, that will extrapolate to 0,002 * 30 * 60 = 3600W power. So in first i need a statistic-writer that writes every delta between 2 values. Currently i do the following wich is not functional:

- platform: statistics
  name: "Power Wattage 2 sec. average"
  unique_id: statistics_power_wattage_2sec_avg
  entity_id: sensor.smart_meter_grid_import_watt_hours
  state_characteristic: change
  sampling_size: 2
  precision: 0

sensor.smart_meter_grid_import_watt_hours total increasing - Wh meter counter total

What i am doing wrong? What state_characteristic and sampling-size should i use to get delta values for each update? - Again: the counter updates every 2 seconds.