Croydon was the second town to have experimental postcodes, introduced in 1966 (Norwich having been the first). The system originally introduced included the postcode area CRO (letter 'O'), while Norwich used NOR for its equivalent. It was decided that the outward (first) part of a postcode should be alphanumerical, so CRO became CR0 (digit '0') and NOR became NR1. The CR1 postcode has not been introduced, making CR the only postcode area with a district 0 but not a district 1. Another lasting consequence of the experiment is that CR9 is allocated to large users, the only UK post town to have its high-volume addresses segregated non-geographically.