Growth Rate on my Castor Bean

This is my first year growing castor beans and so far I'm impressed. I got this plant about 15 days ago (2 weeks!) for 3 dollars and it's already grown so much! Here's a look at it's life in my yard so far. It seems to get bigger  by the day!
*** Keep in mind though that unfortunately, each of these pictures are more zoomed in than the last so the plant appears to be growing even larger than it actually is. Sorry about that!
I determined it's growth rate by competing it to the bricks and to the size of the begonias.

July 10, 2014

July 20, 2014

July 25, 2014