The Abacus and the Cross

• http://www.dailymotion.com/video/xm8nij_osher-the-abacus-and-the-cross_lifestyle
• https://vimeo.com/84700838
• http://www.maa.org/publications/maa-reviews/the-abacus-and-the-cross-the-story-of-the-pope-who-brought-the-light-of-science-to-the-dark-ages