Find the Midpoint Using the Compass ONLY (Mascheroni's Method)

Given two points A and B in the plane, how can you find the midpoint using a compass ONLY? Please try "View-->Protocols" to see how it works. Isn't it Beautiful!

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Questions

1) Why does it work?
2) How is it related to the traditional compass-straightedge approach?
3)Can you create a new midpont tool using the "Bubbling Method'?

Reference
http://mathworld.wolfram.com/MascheroniConstruction.html

Lingguo Bu, Created with GeoGebra