INTERFACE {{p}}if_meter_reading PUBLIC.
  TYPES ty_meter_id TYPE c LENGTH 10.
  TYPES ty_reading_date TYPE d.
  TYPES ty_value TYPE i.
  TYPES:
    BEGIN OF ty_reading,
      meter_id      TYPE ty_meter_id,
      reading_date  TYPE ty_reading_date,
      reading_value TYPE ty_value,
    END OF ty_reading.
  TYPES tt_readings TYPE STANDARD TABLE OF ty_reading WITH DEFAULT KEY.
  TYPES:
    BEGIN OF ty_result,
      meter_id      TYPE ty_meter_id,
      opening_value TYPE ty_value,
      closing_value TYPE ty_value,
      consumption   TYPE ty_value,
    END OF ty_result.
  TYPES tt_result TYPE STANDARD TABLE OF ty_result WITH DEFAULT KEY.
  METHODS calculate
    IMPORTING it_readings      TYPE tt_readings
    RETURNING VALUE(rt_result) TYPE tt_result.
ENDINTERFACE.