In this paper we present a solution to the problem of visualising large amount of hierarchical information structures on small computer screens. Our solution has been implemented as a prototype for mobile use on a hand-held computer using Microsoft Pocket PC with a screen size of 240x320 pixels. The prototype uses the same information as service engineers use on stationary computers. The visualisation technique we used for displaying information is based on fisheye technique, which we have found functional on small displays. The prototype is domain independent; the information is easily interchangeable. A consequence of the result presented here is that the possibility of using hand-held computers in different types of contexts increases.