This is the commercial version of the electrical rainfall recorder made by Casella, London, circa 1960 and used by the National Rivers Authority prior to the introduction of automatic weather stations. This instrument has an oak and glass case with a hinged lid and brass handle with a  weekly clock recording up to 2"of rain before returning, via a piston arrangement, to zero at the bottom of the chart. There is also a GPO counter fitted to the base which totalizes the each 0.02". The instrument receives an electrical pulse from an "8 rain guage incorporating a tipping bucket mechanism (not supplied, but generally available). 
Quite rare now and nice collectors item!