To age the notes, between 40 and 50 prisoners stood in two columns and passed the notes among them to accumulate dirt, sweat and general wear and tear. Some of the prisoners would fold and refold the notes, others would pin the corners to replicate how a bank clerk would collect bundles of notes. British names and addresses were written on the reverse, as happened with some English notes, and numbers were written on the front – duplicating how a bank teller would mark the value of a bundle. Four grades of note quality were introduced: grade 1 was the highest quality, to be used in neutral countries and by Nazi spies; grade 2 was to be used to pay collaborators; grade 3 was for notes that were to be possibly dropped over Britain; grade 4 were too flawed to be of use and were destroyed.