because the distances stated at that time were frequently based on imprecise estimates, zürner had to survey the distances afresh or verify existing data. to achieve that he designed a survey vehicle in the shape of an electoral saxon baggage coach. each revolution of the rear wheel of the coach with a circumference of one dresden rod ("dresdner rute"), i.e. 4.531 metres, was transmitted to a mechanical counter in the coach by means of a chain. zürner's assistants used a measuring cart in the shape of a wheelbarrow for those tracks unsuitable for a coach, which likewise measured the distances by the turning of a wheel and which was carried as the so-called "fifth wheel on the wagon" ("fünftes rad am wagen") in a case on the surveying coach. both methods enabled a very accurate survey of roads.