 The English and Viennese square pianos were built in many different designs, including within the action as well as general appearance, from roughly 1760.Because of the competitive industry and relative youth of the instrument design itself, experimentation ensued in the early years, creating a range of moderators (sound-altering effects) and other technical devices (knee levers; hand stops) not seen today.In London, the explosion of the trade is generally attributed to the maker Zumpe.