http://www.sowacs.com/sensors/gypsum.txt

For more on Gypsum Blocks check out these sites

Making Gypsum Blocks

http://www.sowacs.com/sensors/makegypsumblocks.html

In General

http://www.sowacs.com/sensors/gypsum.html

Users of Gypsum blocks should be aware that all blocks are not the same, they should be selected according to your needs as their construction and accuracy can vary greatly.