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While looking at the documentation for a Casio calculator, I noticed that it had base conversion support for pental. Has anyone seen that feature in other calculators? What might it be used for?

Some Sharps (like the 506W) have that feature. I've assumed it's mostly fluff.


Maybe I have become rusty in my grey cells, but what is a "pental"



I assume that pental means base 5 whereby decimal 5 would be represented by 10 and decimal 10 would be 20. I've never seen a computer that uses base 5. I've worked on several that use base 2, base 8 and base 16.


I think the most common use of the pental numbering system is by prisoners in institutions of incarceration. Prisoners mark the passage of days by marking on the wall. Days are counted using four vertical strokes for the first four days. The fifth day is marked with a diagonal line across the group of four. After that, a new group of five is started.

Here's an example from a modern pentaltentiary. ;)

Mark Hardman

Houston, TX

Edited: 11 Mar 2005, 9:31 p.m.

Actually, that's a unary numeral system.

Is it Hard, man, to Mark the walls?



Which Casio calculator? The latest Sharps, which include the EL-506W, are the first calculators I've seen with base 5.


based on what I see and teach, the 'number' that describes a 'base number' expresses the quantity that cannot be represented in the 'base number' with a single algarism. You see, octal, base eight, uses eight algarisms and the last one is seven. The decimal quantity 'eight' is represented as '108' or '10o'.

Pental refers to a base number with five algarisms, being them 0, 1, 2, 3 and 4. The decimal quantity 'five' should be expressed '105'. Intriguing!


Luiz (Brazil)

You're right. It was a Sharp EL-506WB. I had it confused with another calculator.

Isn't the abacus a base-5 machine?