function electrical_mobility_1_air (millibar, Celsius, d {nm} : real) : real;
  {cm2 V-1 s-1, singly charged particles of density 2 g/cm3 in air,
   uses external function "electrical_mobility_air"}
   begin electrical_mobility_1_air :=
         electrical_mobility_air (millibar, Celsius, 2, 1, d);
   end;