Scale from point

Zoom clones from a centre point. You can drag the centre point (red dot) around and set the slider to the size it should scale at from the centre point.

It divides the ideal size by 100 so it is a decimal scale factor; that way I can just multiply the original size and position by the scale factor.

Uses a classic Scratch-style ease function for a transition effect:

(ScratchBlocks)
set [scale factor v] to (((ideal scale factor) - (scale factor)) / (3))