[GSBN] Perms and Grains?

[Chris Magwood]

Hi all,

I'm trying to compare the permeability of two different sheathing 
products. One tells me that it is rated at 37 imperial perms and the 
other says it is 5 grains/h-ft2-in (Hg min).

Can anybody tell me what the second rating means, and how it might 
compare to imperial perms?

Thanks!

Chris

-- 
Chris Magwood
Director, Endeavour Centre
www.endeavourcentre.org