The bleeding time test measures the time taken for blood vessel constriction and platelet plug formation to occur. No clot is allowed to form, so that the arrest of bleeding depends exclusively on blood vessel constriction and platelet action. To perform the test, pressure is maintained throughout the test by inflating a sphygmomanometer cuff on the upper arm. The dorsal surface of the forearm is then cleaned, and the bleeding time device placed onto the skin and the trigger is depressed. At 30-second intervals, the flow of blood is blotted with filter paper. The time from puncture to cessation of bleeding is then recorded as the bleeding time. Normal values depend on the device used and other parameters, but are around 2 to 9 minutes.