In source messages, we can find information that confirms how widespread and important to ancient Romans was counting on the fingers. An example is Quintilian, who mentions that knowledge of numbers is needed not only for speakers but also for anyone who can write. A speaker who can not perform basic calculations shows hesitation and shows abnormal gestures with his fingers immediately loses confidence.
Another author who mentions presenting numbers with fingers pattern is Pliny the Elder, who is one of his texts summons a stone statue of Janus, who was supposed to present the number of days in a year, i.e. 365, with both hands.
Bede the Venerable – description of the ancient counting system on the fingers
Thanks to Bede the Venerable, who copied a list of Roman characters in the early Middle Ages from ancient documents and described them in De Temporum Ratione, we know how particular numbers were presented. On the basis of these accounts in the fifteenth century, Luca Pacioli made an illustration depicting the Roman method of counting on the fingers.
The credibility of the information provided by Bede the Venerable can be confirmed by the Roman tesseres from the first three centuries CE, on which the obverse showed the hand in the right position, while the reverse was engraved with the number shown in the Roman notation. Most of the shows on coins, except for 10 and 30, exactly match the messages of the monk.
However, how have the numbers been probably presented?
When saying one, bend the little finger of the left hand to the middle. At the two numbers, the ring finger is bent in the same way, while the middle finger is bent for three. By showing four, the smallest finger straightens anew, creating a horn-like gesture. In the case of five the ring finger is also straightened, all fingers of the left hand, except the middle one, are straightened. In the case of six, the only innermost toe is the ring finger, the others remain straight.
Numbers seven, eight and nine are shown almost identically as numbers one, two, three, with folded fingers (with a seven small finger, with a small eight and a small ring, with a small, cordial and middle nine) are not directed to the centre of the hand, but to the edge between the metacarpus and the fingers.
For numbers from 10 to 90, the thumb and forefinger are primarily used.
When you say twenty, place the tip of your thumb on the centre joint of your index finger. At thirty, the tips of the thumb and index finger are joined together in a light grip. Forty presents itself by placing the thumb with its inner side close to the side or back of the index finger, keeping both of these fingers straight. With the fifty number, bend at right angles to the thumb, which then becomes similar to the Greek gamma letter. By showing the sixty number, the thumb stays in the same position but is covered by the index finger. In the case of the seventy number, the thumb remains in the flexion, but its toenail touches the middle joint of the index finger (this one also remains bent), filling the hole that appeared when displaying the previous number. At eighty the thumb straightens up, while the index finger is wrapped around its tip. In turn, showing the number ninety the tip of the bent index finger should be in the base of the straightened thumb.
Numbers from 100 to 9000 are shown in a similar way to numbers from 1 to 90, the only difference is the hand you use. To show numbers larger than 10,000, other parts of the body were also used – for example, where the heartbeats to picture the number 300,000.
Left and right hand
Numbers less than 100 were shown with the fingers of one hand, from 100 to the other. In this way, up to 10,000 could be counted with both hands. Probably smaller numbers were presented using the left hand, while the larger ones were shown using the right hand. It can be proved by a fragment of one of the satire Juvenal, where he indicated that Nestor, having crossed the hundred, counted his years on the right hand.