Step 3 – doing a countdown
To use a reaction timers, we're going to want to start with a countdown.
After the countdown, you're going to need to press button b as fast as you can.
But first, we need to learn how to do a countdown.
Once you have the program written, send it to the micro:bit and press button a a few times. You should see a countdown followed by a diamond being shown. That's your command to start pressing button b.
