docs: def _get_value_opc_attr(self, attr_name, prec_decimals=2):
          """Return sensor attribute with precission, or None if not present."""
          try:
              value = getattr(self, attr_name)
              if value is not None:
                  return round(value, prec_decimals)
          except I2cVariableNotImplemented:
              pass
          return None