G.GCI.2 Angle Formed by Chord & Tangent (I)

In the circle in the applet below, the pink angle is said to be an angle formed by a chord and a tangent. Interact with this applet for a few minutes. As you do, be sure to change the locations of the BIG POINTS each time before re-sliding the slider! How does the angle formed by a chord and tangent relates to the central angle with the same arc?

Quick Demo: 1:33 sec to END (BGM: Edward Shearmur)