What rectangle(s) work?

[fncll]

Earlier tonight I folded this mandala:
http://entrevalesemontanhas-origami.blo ... -tayo.html

The diagram indicates to use an A9 rectangle (52x37mm)

I see that someone else folded it from an A8 (74x52mm):
http://www.flickr.com/photos/62572859@N08/8532707967/

Is there a way to know, through some math/geometry magic, what rectangle proportions will work for this model (short of trying each rectangle manually)?

[camicazi]

any A works, as they have identical proportions. A9 is just a A8 cut in half, and if you enlarge it(A9), it will be an exact copy of an A8 paper. If you cut an A1 paper in half 7 times you will get an A8 paper, so if you want to get a giant version of the model you can use A3 or A4 as long as they can withstand the weight
Edit: Found a picure that explains it better http://2.bp.blogspot.com/-LLrkNz2dNy4/U ... f_24kB.gif

[tschobigami]

generally A-sized rectangles have the proportions "1xsqrt(2)" so just take a rectangle with these proportions and it will work
here is how to get these A-sized rectangles from a random rectangle
http://www.nickrobinson.info/origami/te ... angles.htm