Abstract: There is provided an apparatus for measuring variations in pressure including a container for housing a volume of liquid and an indicator float to be movably supported by the liquid therein. The float is to have a hollow interior portion for maintaining a volume of compressible fluid, and is vertically movable within the container. The apparatus further includes a variable buoyancy equilibrium force device for automatically offsetting buoyant forces created by the compressible fluid within the float, whereby the equilibrium force is automatically varied in response to changing buoyancy of the float corresponding to changing ambient pressures. In a preferred embodiment, the variable buoyancy equilibrium force device comprises a flexible ballast structure attached to an adjustable support above the float, and wherein excess length of the ballast collects in a ballast retainer on the upper portion of the float.