Electronic display of an event in which 4 cosmic ray muons have passed through the IMB (Irvine- Michigan- Brookhaven) proton decay detector located 600 metres underground in the Morton salt mine near Cleveland, Ohio. The display is a computer graphic representation of the detector, which consists of a massive tank containing 21 cubic metres of ultrapure water, its walls lined with photomultiplier tubes which detect faint flashes of Cerenkov light emitted by the passage of charged particles. The display shows the photo- multiplier tubes triggered by the Cerenkov light in the form of coloured stars & slashes.