How a slow acting sprinig works?

I want to know how a slow acting spring works. I'm doing a small project on door opening mechanism. i want to install this to that. here's the link:
https://www.youtube.com/watch?v=aLc9FCA40z8

any Information like working, or calculations are welcome..

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https://www.google.com/patents/US6178085

The really cool part, is the calculator in the video looks to be an exact match to the images in the patent drawing.

 
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