An abacus is a digital device, but it's not a binary digital device obviously.
Since it is very common for an abacus to have 5 beads per pole
These are "bi-quinary" abacuses that have two rows of beads, the bottom row is 0-4 and the top row is either 0 or 5.
Computers weren't always binary, though. https://en.wikipedia.org/wiki/ENIAC - looks like it was decimal based as it was electronically (with tubes) working like an adding machine.
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An abacus is a digital device, but it's not a binary digital device obviously.
These are "bi-quinary" abacuses that have two rows of beads, the bottom row is 0-4 and the top row is either 0 or 5.
Computers weren't always binary, though. https://en.wikipedia.org/wiki/ENIAC - looks like it was decimal based as it was electronically (with tubes) working like an adding machine.