This unit will have   two separate sockets to fix 10 channel G.D. Tube modules (magazine). One socket for Fetex type & another for Pouyet type G.D.tube magazine. There will be 10 pairs of switches to select individual GD Tube. This individual tube is tested without removing it from the module.   After selecting particular GD Tube, that tube is subjected to different  modulated signal. For low signal gas in the G.D. tube will not discharge ,hence we will not get any alarm .Where as  for High signal , gas will discharge and we will get alarm. With this tester we will come to know whether GD tube is short or open or ok. . Faulty G.D. tube can then be replaced  and  entire magazine can be reused.