A computer-implemented method for calculating a liquid surface plane location in a containment vessel, comprising: (a) storing a first set of data comprising a solid model representation of said containment vessel; (b) storing a second set of data representing a spatial orientation of said containment vessel; (c) storing a third set of data representing a magnitude and direction of acceleration of said containment vessel; (d) storing liquid volume data representing a volume of liquid (12,14,16) in said containment vessel; (e) deriving a first set of image data representing a surface plane of said liquid in said containment vessel, said first set of image data being a function of at least said first through third sets of data and said liquid volume data; and (f) displaying said first set of image data in intersecting relationship with a second set of image data representing said containment vessel having said spatial orientation; characterised in that said deriving step comprises: selecting a current guess for the location of said liquid surface plane; determining the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location using regularized solid modeling operations; comparing the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location to the volume of liquid (12, 14, 16) represented by said liquid volume data; if the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location does not match, within a given tolerance, the volume of liquid (12, 14, 16) represented by said liquid volume data, using a numerical method to improve the current guess for the liquid surface plane location; and repeating steps through until the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location matches, within the given tolerance, the volume of liquid (12, 14, 16) represented by said liquid volume data; wherein said numerical method comprises finding successively better approximations to the zero of a function equal to a difference between the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location and the volume of liquid (12, 14, 16) represented by said liquid volume data. (a) storing a first set of data comprising a solid model representation of said containment vessel; (b) storing a second set of data representing a spatial orientation of said containment vessel; (c) storing a third set of data representing a magnitude and direction of acceleration of said containment vessel; (d) storing liquid volume data representing a volume of liquid (12,14,16) in said containment vessel; (e) deriving a first set of image data representing a surface plane of said liquid in said containment vessel, said first set of image data being a function of at least said first through third sets of data and said liquid volume data; and (f) displaying said first set of image data in intersecting relationship with a second set of image data representing said containment vessel having said spatial orientation; selecting a current guess for the location of said liquid surface plane; determining the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location using regularized solid modeling operations; comparing the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location to the volume of liquid (12, 14, 16) represented by said liquid volume data; if the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location does not match, within a given tolerance, the volume of liquid (12, 14, 16) represented by said liquid volume data, using a numerical method to improve the current guess for the liquid surface plane location; and repeating steps through until the volume of liquid (12, 14, 16) below the current guess for the liquid surface plane location matches, within the given tolerance, the volume of liquid (12, 14, 16) represented by said liquid volume data;