At Amsterdam Zuid it switches from third rail to pantograph and catenary wires. Such vehicles can be fitted with either a pantograph or trolley pole. Warns driver to lower the locomotive's pantograph. The cars contacted this wire through the use of a trolley pole or a pantograph. Hollerith developed the pantograph "keyboard punch". When molding improved somewhat, molded cylinders were used as pantograph masters. In 1977 W2 546 was fitted with an experimental Siemens pantograph. The locomotives were fitted with a pantograph as well as pick-up shoes. The original use of the pantograph was for copying and scaling line drawings. Some used the same pantograph for multiple electrical systems. Another difference was the lack of a second pantograph. A system which monitors the integrity of the pantograph. It introduced the single-arm pantograph in 1955. These can be noted by the positioning of the pantograph. It introduced in 1923 its first pantograph.