Here we define a few things which will ease our introduction into the use of the abacus.
The correct position of the abacus is as shown above in the diagram.
The CROSSBAR is that which separates the two sets of beads.
The TOPBEADs are the set of two beads above the CROSSBAR.
The UNITBEADs are a set of five beads below the CROSSBAR.
STACKing is the process where we place a bead against the CROSSBAR
WITHDRAWing is the process where a bead is taken off a stack (of beads against the CROSSBAR)
When a UNITBEAD is moved to rest against CROSSBAR, it represents the number one (1). When two UNITBEADS are moved to rest against a CROSSBAR it representw the number two (2), and so on.
When a TOPBEAD is made to rest against the CROSSBAR, it represent the number five (5). Since there are two, the other is rarely used, but if it is, then the value of 10 is expected.
Note that the abacus works in base 10, as in normal counting. The rods indicate the various units of counting in base 10. That is, starting from an arbitary rod, units, and continuing left, tens, hundreds, thousands... However, to the right of the units rod, decimal fractions are represents, tenths, hundredths, thousandths etc.
By moving the beads against the bar, they represent the number desired.