As ythe abacus is a counting device used to count up to ten, the minimum number of wires and beads would be 1 wire and 1 bead allowing you to count 1 the usual number of beads on a wire is ten allowing the counting of up to ten. To continue counting an additional wire with 10 beads would be added for 100's, 1000's, 10,000's etc. so an abacus which can count to 10,999 would have four wires Hope this helps. Further info on the Abacus can be found in Brewers Phrase and Fable.
