An electrical telegraph consisted of two or more geographically separated stations (often called telegraph offices) connected by wires, usually supported overhead on utility poles. There were many different electrical telegraph systems invented, but the ones that became widespread fit into two broad categories. The first category consists of needle telegraphs in which a needle pointer is made to move electromagnetically with a pulse of electric current from a battery or dynamo down the telegraph line. Early systems used multiple needles requiring multiple wires. The first commercial system, and the most widely used needle telegraph, was the Cooke and Wheatstone telegraph, invented in 1837. Early equipment sets used five needles to point to the letter being transmitted, but the cost of installing wires was more economically significant than the cost of training operators so a single-needle system with a code that had to be learned became the norm.