I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "Devices have been used to aid computation for thousands of years, mostly using one-to-one correspondence with fingers. The earliest counting device was probably a form of tally stick. Later record keeping aids throughout the Fertile Crescent included calculi (clay spheres, cones, etc.) which represented counts of items, probably livestock or grains, sealed in hollow unbaked clay containers. The use of counting rods is one example."? 

What isn't a type of aid between clay spheres, grains and cones?