Instructions:

• Drag the poles (crosses) and zeros (circles) and watch the amplitude response change.
• To add a new pole or zero click (don't drag) on the z-plane (left half of the applet).

Why I did this:

• I felt like doing some Java programming.
• I was discussing something similar with a friend.
• That friend showed me that MATLAB does something similar.

Notes:

• Very early stages.
• No axis labels.
• The response plot is linear and not on a log (dB) scale.
• No access to numeric values of poles and zeros
  
• But its a start!