EKI Reaction Tester Soldering Practice Kit (Beginner Skill Level)Beginner skill level kit, little or no previous knowledge of electronics required. Basic soldering techniques required for circuit board assembly. Once assembled, the Stop Action Reaction Tester flashes an LED every 2 seconds for approximately 0. 1 second. If you release the pushbutton at the exact time that the LED is lit, the LED will "freeze". Since the "ON" time is so short you cannot wait to see the LED but must anticipate it's flash rate.