ρx	density of the hydrometer at selected scale mark x.
ρL	density of reference liquid.
ρa1	density of air during mass determination of hydrometer in air (ma).
ma	mass of the hydrometer in air.
mL	apparent mass of hydrometer immersed in the liquid up to scale mark x.
g	acceleration due to local gravity.
π	Pi value = 3.14159265.
D	diameter of the hydrometer stem at the selected scale mark x.
γx	surface tension coefficient of the liquid where hydrometer is used.
γL	surface tension coefficient of reference liquid.
α	thermal expansion coefficient of hydrometer (usually glass).
tL	temperature of reference liquid.
t0	nominal temperature value of hydrometer's scale.
εd	error due to hydrometer's resolution.
mp1	mass standard used during mass determination of hydrometer in air.
mp2	mass standard used during apparent mass determination of hydrometer immersed in liquid.
ρp1	density of mass standard used during mass determination of hydrometer in air.
ρp2	density of mass standard used during apparent mass determination of hydrometer immersed in liquid.
ρa2	density of air during apparent mass determination of hydrometer in liquid (mL).
Δm1	mass difference during weighings in air.
Δm2	mass difference during weighings in liquid.
Cg	gravity correction due to difference in centre of mass.
εd(bal)	error due to resolution of the balance.
∂g/∂h	vertical gravity gradient.