A fire suppression system comprising: a tank (22; 410) having a first port (40; 420) and an interior; at least one of a fire suppressant and a fire suppression propellant in the interior; a discharge assembly (46; 422) mounted to the first port and comprising a discharge valve (48; 424); and a system for measuring the fire suppressant or fire suppression propellant quantity, the system for measuring the fire suppressant or fire suppression propellant quantity comprising: a base; a top plate positioned to support a tank of said fire suppressant or fire suppression propellant; a plurality of springs positioned between the top plate and the base to support the top plate atop the base, the plurality of springs positioned to support the top plate along a range of motion between an extended condition and a retracted condition; a first magnetic member mounted to the base; a second magnetic member mounted to the top plate so that a spacing between the first magnetic member and the second magnetic member decreases as the top plate moves from the extended condition to the retracted condition, at least one of the first magnetic member and the second magnetic member being a permanent magnet; a magnetic field sensor positioned to detect changes in a magnetic field associated with changes in said spacing; and control electronics having memory storing: a look up table with data for a combination of tank mass and tank position on the scale; and/or a stored function relating sensor output to mass in order to estimate the degree of off-center load distribution and estimate the mass. a tank (22; 410) having a first port (40; 420) and an interior; at least one of a fire suppressant and a fire suppression propellant in the interior; a discharge assembly (46; 422) mounted to the first port and comprising a discharge valve (48; 424); and a system for measuring the fire suppressant or fire suppression propellant quantity, the system for measuring the fire suppressant or fire suppression propellant quantity comprising: a base; a top plate positioned to support a tank of said fire suppressant or fire suppression propellant; a plurality of springs positioned between the top plate and the base to support the top plate atop the base, the plurality of springs positioned to support the top plate along a range of motion between an extended condition and a retracted condition; a first magnetic member mounted to the base; a second magnetic member mounted to the top plate so that a spacing between the first magnetic member and the second magnetic member decreases as the top plate moves from the extended condition to the retracted condition, at least one of the first magnetic member and the second magnetic member being a permanent magnet; a magnetic field sensor positioned to detect changes in a magnetic field associated with changes in said spacing; and control electronics having memory storing: a look up table with data for a combination of tank mass and tank position on the scale; and/or a stored function relating sensor output to mass in order to estimate the degree of off-center load distribution and estimate the mass. a base; a top plate positioned to support a tank of said fire suppressant or fire suppression propellant; a plurality of springs positioned between the top plate and the base to support the top plate atop the base, the plurality of springs positioned to support the top plate along a range of motion between an extended condition and a retracted condition; a first magnetic member mounted to the base; a second magnetic member mounted to the top plate so that a spacing between the first magnetic member and the second magnetic member decreases as the top plate moves from the extended condition to the retracted condition, at least one of the first magnetic member and the second magnetic member being a permanent magnet; a magnetic field sensor positioned to detect changes in a magnetic field associated with changes in said spacing; and control electronics having memory storing: a look up table with data for a combination of tank mass and tank position on the scale; and/or a stored function relating sensor output to mass in order to estimate the degree of off-center load distribution and estimate the mass. a look up table with data for a combination of tank mass and tank position on the scale; and/or a stored function relating sensor output to mass in order to estimate the degree of off-center load distribution and estimate the mass.