Magical Wall Calendar Hidden Historical Facts

Do you want to Know what happened on this day of history?
This calendar will tell you.
How magic? Each black block represents one day, this would not be surprising, but when you touch it, black surface (heat sensitive coating) will disappear, shows the history of what happened today. 
For example, touch on the day of January 27th, you will be surprised to find that the same day in 1880 Edison invented the light bulb, when the temperature disappeared, the block will change back to black.
You don't need to check this on Internet.
So, waht do you want to know about today of history?
By the way, you can write your daily to do's on the other space of the calendar. It's useful, right?
Link:http://www.tinydeal.com/heat-sensitive-thermosensitive-pvc-magical-wall-calendar-p-145010.html