The u. s. army commissioned a study to assess how deeply a bullet penetrates ceramic body armor ("testing body armor materials for use by the u. s. army–phase iii," 2012). in the standard test, a cylindrical clay model is layered under the armor vest. a projectile is then fired, causing an indentation in the clay. the deepest impression in the clay is measured as an indication of survivability of someone wearing the armor. here is data from one testing organization under particular experimental conditions; measurements (in mm) were made using a manually controlled digital caliper: