A synergistic improvement of a precious metal assaying device with its associated electronic decoding algorithms further employing a precise feed of an electrolyte from a disposable flexing cartridge and through porous media for conveying electrolyte to create a reproducible electrochemical contact by a wetting action between a reference electrode in the assaying device and an external specimen under test where the electrolyte is passed through a novel slit diaphragm permitting efflux of electrolyte and reflux of unused electrolyte that results in a self-cleaning flush of the assaying device. The synergistic slit diaphragm permits the flow of electrolyte from the flexing cartridge in response to the positive pressure and the cleansing return of unused electrolyte on negative pressure of the cartridge, thereby solving a contamination problem which was a major shortcoming in such assaying devices.