API MPMS 3.1A pdf download.Manual of Petroleum Measurement Standards Chapter 3—Tank Gauging 3.1A.1 Scope This standard describes the following: (a) the procedures for manually gauging the liquid level of petroleum and petro- leum products in non-pressure fixed-roof, floating-roof tanks and marine tank vessels, (b) procedures for manually gauging the level of free water which may be found with the petro-...