Bill books come with duplicate and triplicate copies. Duplicate copy means it will be 1+1 booklet i.e. 1 parent copy and 1 duplicate copy. Triplicate copy means it will be 1+2 booklet i.e. 1 parent copy and 2 duplicate copies. These books and vouches are widely used almost in all companies which have not yet shifted to POS invoicing system which generates the bill automatically.