Advice On Glass Shelf Supports

I bought a couple of ex MFI glass shelves off Ebay and got one ok but awaiting a replacement for the other as it was in bits . They are 800mm x 200mm x 6mm . I have bought 6 brackets which are 110mm deep similar to http://www.sdslondon.co.uk/product/10070-glass_or_wood_shelf_support_5_32_mm.html
but I'm not sure if I should use 3 per shelf or if 2 will do.
I've been Googling to see if I can find suggestions for how many brackets are needed for certain lengths but so far haven't found anyhting . Any ideas ?
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Stuart B wrote:

http://www.sdslondon.co.uk/product/10070-glass_or_wood_shelf_support_5_32_mm.html
If supported at the ends, with a uniform load of 10 lbs per foot, the shelf would only sag by 1.21mm.
http://www.woodbin.com/calcs/sagulator.htm
--
Dave - The Medway Handyman
www.medwayhandyman.co.uk
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On Sun, 03 May 2009 19:49:12 GMT, "The Medway Handyman"

That's useful.Not seen that site before .Thx
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On Sun, 03 May 2009 20:50:11 +0100, Stuart B
Mine is better
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