Underground gravity observations in deep coal mines using the conventional gravity meters Worden (type Master) and LaCoste‐Romberg (model D), both of which have been adapted to the fire damp regulations, can be accurate to ± 10 and ± 3 μgal, respectively. For underground determination of the vertical gradient of gravity the LaCoste‐Romberg meter is used together with a specially designed measuring tower. Using this euipment an accuracy in tower gradient observations of ± 30 E was obtained.
To apply the equipment to precision gravity observations in underground situations an additional correction, i.e. a gallery correction, is needed. High accuracy in correction is achieved by a new method of three‐dimensional modelling. The gravity effect is computed for bodies with a surface approximated by triangular elements, which are generated from corner points of the body. The combination of gallery correction with tower gradient data leads to a new method for in situ density determination. It offers the possibility of horizontal instead of vertical density profiling.
To demonstrate the effectiveness of the developments in underground observations the localization of a pump room is presented. Microgravity and tower gradient observations were carried out to detect the cavity. The horizontal gradient was also calculated to give a more reliable location.
An interactive system must be designed for usability. But usability is often described through a number of heuristics that are difficult to use directly in the design process. The paper discusses how the software engineer may design for good usability. The most important usability heuristics are related to measurable user interface and software properties which the developer can use in the design process.
KeywordsUsability heuristics, software properties of user interfaces.
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