Sounds as easy as counting on your fingers and toes.
Here is a small excerpt from the instruction booklet:
‘A’ beads have each the value of ‘5’ ‘B’ beads each ‘1’. Numerical value are put into effect, when ‘A’ beads are pushed down and ‘B’ beads are pushed up, each to the crosspiece. Black points put on the crosspiece except three reeds represent unit. Suppose that some black point is the unit place of one, the next left and right points shows each 1,000 and 0.001. In case of addition and subtraction, they have important influence, but in case of multiplication and division, they are not so, vital. Why have they not so much effect on multiplication and division? You can understand later.
And so boys and girls, that is how the financial crisis happened. The Poobahs of finance were obviously trying to use sorobans and could not figure out the instructions.