Replica made of bronze. Measures: 125 mm wide, 80 mm height.
 

#ab96 1,000,000 100,000 10,000 1,000 100 10 1 ounce fractions of an ounce

1/2 ounce   1/4 ounce   1/3 ounce

From left to right each of the seven grooves represent a power of 10. They are divided into a lower part containing four sliding counters and a shorter upper part containing only one. Each of the four counters have the value of one according to their power to 10. The counters in the upper grooves represent five units in the order of that groove. So you can display the value 9 in each of the grooves. Starting from the right the three grooves represent ounces and fractions of them. More details you'll find at the references  Georges Ifrah, page 111-113 and  Karl Menninger, page 226-228. The basic idea of four lower and one upper counter was probably transferred to the Asian abacuses. But it is not sure that the Roman abacus was the direct ancestor of the form of abacus, which is still used in East-Asia (China, Japan, Korea). Referring to Chinese and Japanese historians there are some indications that the development of an abacus occurs in the East (India, China) and in the West independently nearly at the same time (Kojima 1963). Unfortunately the results of studying this literature are confusing.