The Sumerians used a numerical system based on 1, 10 and 60. The way of writing a number like 70 would be the sign for 60 and the sign for 10 right after. This way of counting is still used today for measuring time as 60 seconds per minute and 60 minutes per hour. Cuneiform script is one of the earliest known systems of writing. Emerging in Sumer in the late 4th millennium BC, cuneiform writing began as a system of pictographs. Cuneiform documents were written on clay tablets, by means of a blunt reed for a stylus. The impressions left by the stylus were wedge shaped, thus giving rise to the name cuneiform "wedge shaped", from the Latin cuneus "wedge".