diff --git a/code/reaction-timer.py b/code/reaction-timer.py
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+from microbit import *
+import random
+
+# Show animation for random time
+display.show(Image.ALL_CLOCKS, loop=True, wait=False, delay=100)
+sleep(random.randint(500, 5000)) 
+
+# prompt user to press button
+display.show(Image.ARROW_E) 
+start_time = running_time() # set start time
+
+# wait for button_b to be pressed 
+while not button_b.was_pressed(): 
+    sleep(20)
+
+# record time taken to press button
+end_time = running_time() 
+
+# calculate and scroll reaction time
+reaction_time = end_time - start_time  
+display.scroll(str(reaction_time)) 
+
+# reset if button a is pressed
+display.show(Image.ARROW_W) 
+while not button_a.was_pressed(): 
+    sleep(20)
+reset()
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diff --git a/reaction-timer.md b/reaction-timer.md
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+---
+title: "Reaction Timer"
+layout: text-width-sidebar
+
+# Meta description for google and sharing
+meta-description:  "microbit game in python to time the reaction speed of a user pressing a button."
+
+# simple description for TOC
+simple-description: "Reaction Timer"
+
+#############
+## Options ##
+#############
+
+share: true
+comments: yes
+author: romilly
+
+###############################
+## Program Template Specific ##
+###############################
+
+# Stapline beneath the header
+strapline: "Reaction Timer Game"
+
+# About Box is on the left of the program page
+aboutbox: "A single person game to time the reaction speed of a user's input."
+
+# Difficulty of program: easy, medium or ninja
+cats: medium
+
+date:         2017-02-02T10:20:00Z
+date-updated: 2017-02-02T10:20:00Z
+---  
+
+{% highlight python %}{% include_relative code/reaction-timer.py %}{% endhighlight %}
+
+This is a simple game to show how long it takes a user to press a button. 
+
+* Show an animation of a clock face for a random amount of time
+* Prompt user to press a button
+* Display time taken for the user to press the button
+
+A video will go here.
+
+### Code Explained
+{: .ui .dividing .header}
+
+
+
+#### Import Random
+{% highlight python %}
+from microbit import *
+import random
+{% endhighlight %}
+
+The program uses `random.randint(500, 5000)` to return a random number between 500 and 5000. The random number module must be imported with `import random`. 
+
+The random number between `500` and `5000` is used to tell the microbit to sleep for a random amount of time between .5 and 5 seconds.
+
+
+
+#### Clock Animation
+A clock animation is shown on the microbit before prompting the user to press a button. The code is:
+
+{% highlight python %}
+display.show(Image.ALL_CLOCKS, loop=True, wait=False, delay=100)
+{% endhighlight %}
+
+`Image.ALL_CLOCKS` is a list of all the clock images, eg `CLOCK1`, `CLOCK2`, `CLOCK3`, etc. 
+
+The [microbit micropython documentation gives a complete explaination](http://microbit-micropython.readthedocs.io/en/latest/display.html) of `display.show`: 
+
+In this program, `loop=True` causes all images in the `Image.ALL_CLOCKS` list to repeat. `wait=False` causes the animation to happen the the background.
+
+
+
+#### Calculate Reaction Time
+* `running_time()` returns the amount of time the microbit has been running in milliseconds since the last reset.
+* `start_time` is the time at which the timer began waiting for a user to press button_b.
+* `end_time` is the time at which the user pressed button_b. 
+
+The difference between `start_time` and `end_time` is the time in milliseconds it took for the user to press button_b.
+
+
+
+#### Wait for User to Press Button
+{% highlight python %}
+while not button_b.was_pressed():
+    sleep(20)
+{% endhighlight %}
+
+`button_b.was_pressed()` returns true if `button_b` was pressed since the last time it was called. 
+
+This `while loop` continues while button_b was not pressed. It essentially waits for `button_b` to be pressed.
+
+
+
+#### Scroll Reaction Time
+
+{% highlight python %}
+display.scroll(str(reaction_time))
+{% endhighlight %}
+
+Convert `reaction_time` (the time taken for the user to press the button) to a string and scroll it on the display.
+
+
+
+#### Reset 
+
+{% highlight python %}
+display.show(Image.ARROW_W) 
+while not button_a.was_pressed():
+    sleep(20)
+reset()
+{% endhighlight %}
+
+At the end of the program, an arrow points at `button_a`. A `while` loop waits for the user to press `button_a`.
+
+When `button_a.was_pressed()`, `reset()` is called which restarts the microbit and causes the program to run again. 
+
+
+
+### Next Steps
+
+* It's possible to cheat but pressing `button_b` when the clock animation is showing. Introduce a way of stopping the cheating.
+* Make a two player game.
+
+
+
+### See More
+
+* This program is also [written up here](http://blog.rareschool.com/2017/01/a-simple-reaction-timer-in-micropython.html).
+* The code is available [on github](https://github.com/microbit-and-chips/reaction-timer).
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