Amagat

An amagat is a practical unit of volumetric number density. Although it can be applied to any substance at any conditions, it is defined as the number of ideal gas molecules per unit volume at 1 atm (101.325 kPa) and 0 °C (273.15 K). It is named after Émile Amagat, who also has Amagat's law named after him. The abbreviated form of amagat is "amg". The abbreviation "Am" has also been used. (Wikipedia).