Postal Index Number (PIN) or PIN Code is a 6 digit code of Post Office numbering used by India Post. The PIN was introduced on August 15, 1972. There are 9 PIN regions in the country. The first 8 are geographical regions and the digit 9 is reserved for the Army Postal Service. The first digit indicates one of the regions. The first 2 digits together indicate the sub region or one of the postal circles. The first 3 digits together indicate a sorting / revenue district. The last 3 digits refer to the delivery Post Office.