theory11 — Magic Tricks & the World's Finest Playing Cards

Torn too impromptu

Well you just need a little something in your pocket and if you have that then you can do it whenever I guess. It depends on your version of 'impromptu'.

It is a great effect. Have fun with it.
 
It is amazingly practical and easy to do aswell. Great strolling trick as the reset is instantaneous.

The concept is great however I use to use it with my business cards for reasons that are obvious when you understand the method.