The role of the Armourer is to maintain the small arms, machine guns and Infantry Support Weapons in a unit. They use hand and machine tools, gauges and precision measuring instrucments to inspect, repair and modify weapons and associated equipment to a tolerance of plus or minus 0.04 mm. This is one of the most important jobs in a military unit and especailly an Infantry battalion, which relies upon the Armourer to ensure availability of the weapons at all times.