A storage system comprises a data set storage region for storing a data set containing data and update information for managing this data, and a control section. The hydrometer may include a box structure comprising side walls and a bottom. In a preferred embodiment, the means for processing the program commands comprises a processor operable to implement only those input program commands or sequences of input programme commands as are required to generate the procedural textures of the standardised set. In the first situation a spring, a pressurizable cylinder having a rod attached to a piston, or a pressurizable cylinder with a piston may be connected to the cable and a heavy object; or a weight may be suspended from the cable. One or more outer layers concentrically surround the core and have a cross-sectional area inversely correlated to the inner core so that the overall container closure has an essentially cylindrical profile. The adjustable member is adjustably positionable about the axis of rotation between adjacent stop member positions.