What are the parts of a polygraph machine and functions?

There are three parts of a polygraph machine. They are:

• the cardio-sphygmograph consisting of a blood pressure cuff placed on the arm that remains inflated during the test - measures blood pressure and heart rate
• the pneumograph consisting of two tubes filled with air, one placed around the chest and the other placed around the abdomen - measures respiratory rate
• the galvanograph which consists of electrical sensors attached to the fingertips - records the amount of perspiration produced