function mass_diameter_1_air (millibar, Celsius, Z {cm2 V-1 s-1} : real) : real;
  {nm, singly charged particles of density 2 g/cm3 in air,
   uses external function "mass_diameter_air"}
   begin mass_diameter_1_air :=
         mass_diameter_air (millibar, Celsius, 2, 1, Z);
   end;