A description of the construction and use of the differential analyser has already been given in the Mathematical Gazette by Professor D. R. Hartree (Vol. XXII (1938), page 342); this note arose from the consideration of means of depicting results to problems depending on three dimensions. In using the machine on what are essentially three-dimensional problems (e.g. orbits and trajectories not lying in a plane), results can usually be presented only in tabular form. As a matter of some interest in this field, consideration was given to the possibility of using the machine itself to draw a perspective diagram of such twisted curves in three dimensions. If this were found practicable it was realised that with two such diagrams, representing the space-figure as seen from two points separated by the distance between the eyes, a stereoscope could be used to reproduce a three-dimensional effect.