This handy field tool combines GSA's popular photo scale and geologic time scale. On one side is our Author's Photo Scale, calibrated boldly in centimeters (10) and U.S. inches (4). Includes a GSA seal for fine focus and an evaluation scale for granular material from 1 to 5 millimeters diameter. The reverse side includes the complete GSA Geologic Time Scale. Although legible, the printing on the time scale is small, identical to our wallet-sized time scale; you may need a hand lens to read it!