Liber Abaci
Leonardo Pisano, 1202
Predictis figuris earumque gradibus, secundum materiam superius descriptam, cum frequenti usu bene cognitis, oportet eos qui arte abaci uti voluerint, ut subtiliores et ingeniosiores appareant, scire computum per signa manuum secundum magistrorum abaci usum antiquitus sapientissime inventa.
Once the aforementioned figures and their gradations have been well learned through frequent practice, according to the method described above, those who wish to make use of the art of the abacus ought also to know the reckoning by hand-signs, most wisely devised in ancient times according to the practice of the masters of the abacus, so as to appear more subtle and ingenious.
Que signa sunt hec.
And these are the signs:
Curvatio auricularis digiti sinistre manus super medium palme manus notat 1. Curvatio, quidem, eiusdem cum anulari similiter super mediam volam 2. Cum quibus curvatur medius 3. Curvatio, autem, anularis et medii, super mediam volam 4. Curvatio, vero, medii tantum 5, anularis 6. Positio quippe auricularis sursum super volam 7. Super quem locum cum ponitur auricularis et anularis notantur 8. Positio quidem eorundem cum medio super eundem locum 9.
The bending of the little finger of the left hand onto the middle of the palm signifies 1. The bending of the same together with the ring finger in like manner onto the middle of the palm signifies 2. When the middle finger is bent together with them, it signifies 3. The bending of the ring finger and middle finger onto the middle of the palm signifies 4. But the bending of the middle finger alone signifies 5; of the ring finger, 6. The placing of the little finger upright upon the palm signifies 7. When the little finger and ring finger are placed in that position, they signify 8. And the placing of those same together with the middle finger in the same place signifies 9.
Cum ab extremitate indicis et pollice fit circulus in nodo pollicis denotat 10. Cum pollex et index sunt extensi et tangunt se 20. Cum ab extremitate eorundem fit circulus 30. Cum ponitur pollex super indicem in exteriori parte indicis 40. Curvatio pollicis super principium indicis 50. Curvatio indicis super curvatum pollicem 60. Curvatio indicis super extremitatem extensi pollicis 70. Curvatio itaque indicis super virgulam extensi pollicis 80. Item curvatio totius indicis in se 90.
When a circle is made with the tip of the index finger and the thumb, on the joint of the thumb, it denotes 10. When the thumb and index finger are extended and touch each other, it denotes 20. When a circle is formed from the tips of the same, it denotes 30. When the thumb is placed upon the index finger on the outer side of the index, it denotes 40. The bending of the thumb over the base of the index finger denotes 50. The bending of the index finger over the bent thumb denotes 60. The bending of the index finger over the tip of the extended thumb denotes 70. Likewise, the bending of the index finger over the shaft of the extended thumb denotes 80. And the bending of the whole index finger into itself denotes 90.
Centenaria quoque et miliaria fiunt in dextera manu eodem ordine, scilicet signum unitatis facit 100 in dextera manu; binarii quidem 200; decenarii autem mille et signum nonagesimum facit 9000, ut in sequenti pagina pictis manibus demonstratur.
Hundreds and thousands are likewise made on the right hand in the same order: namely, the sign for one makes 100 on the right hand; that for two, 200; that for ten, however, 1,000; and the sign for ninety makes 9,000, as is shown on the following page by illustrations of hands.
Componuntur itaque in manibus cum his signis omnes reliqui numeri qui sunt a decem usque in decem milia hoc modo: ex signo vigenarii et ex signo ternarii componuntur 23; et ex signo trium milium et ex signo quingentarum componuntur in dextera manu tria milia quingenta. Et sic intelligas in reliquis.
All the remaining numbers from ten up to ten thousand are therefore formed on the hands with these signs in this way: from the sign for twenty and from the sign for three, 23 is formed; and from the sign for three thousand and from the sign for five hundred, three thousand five hundred is formed on the right hand. And so you should understand it for the rest.
Source: Leonardo Pisano, Liber Abaci. Il libro del calcolo. Epistola a Michele Scoto, prologo, indice, capitoli I-IV, ed. Giuseppe Germano and Nicoletta Rozza (Palermo: Paolo Loffredo, 2019), 144–5.