Initially, the Carte orange was only available to workers, who had to supply proof of employment in order to purchase it. This restriction was soon removed, however, and the Carte became very popular: while transit authorities had estimated that 650,000 Cartes oranges would be sold, within 6 months of its introduction 900,000 were in use. According to Michel Margairaz, a historian of Parisian transports, the gap between these figures can be explained due to a problem in the transit authorities' methodology — they assumed that only those public transit users who would save money with the Carte orange would buy one, but this was not to be the case. Many people were attracted to the idea of using Parisian public transports without worrying about tickets or fares, even if it proved to be more expensive.