“Check for Power If the connection to the NAND-gate IC is correct, use a multimeter to measure the output voltage from the start/stop circuit to see whether it’s working correctly. Set your multimeter to measure voltage. Make sure the black measurement lead is connected to the multimeter’s COM socket, and the red measurement lead is connected to the V socket. Touch the tip of the black lead of the multimeter to the negative side of the battery, and touch the red lead to pin 11 on the 4011 NAND-gate IC. You should see a high signal—about 9 V—after clicking the stop button and a low signal—about 0 V—after pushing the start button. If not, check the connections of the SR latch circuit to find the error.”