Courtesy of the MABRC
When taking pictures of your casts to display for others to see, buy a Grid Cutting Mat from Wal-Mart like the one shown here. Lay the cast on it, and you have the measurement grid on it to show the size of the cast.
This is a sewing measuring board that you can buy at Wal-Mart.
The example above is from Chilko Lake BC Canada WSSSG 9-3-2009