Today I found out the symbol on the “pound” or “number” key (#) is also called an “octothorpe”.

The origins of this term date back to the 1960s and 1970s in Bell Labs with the first documented place this word showed up being in a U.S. patent filed by Bell Labs in 1973. The exact etymology of this word isn’t known as the two “eye witness” accounts are contradictory. However, what is known is that it was a term engineers at Bell Labs started using as early as the 1960s when Bell Labs was working on interfacing techniques between computers and telephones.

It was during this time that Bell Labs came up with the now ubiquitous “touch tone dialing”, which added two additional keys to handsets, the “*” key and the “#” key. It is clear the “octo” part was thought up because of the eight points on the symbol. The origins of the “thorpe” (sometimes written “thorp”) are not so clear.

Ralph Carlsen of Bell Labs wrote a memorandum on this symbol upon his retirement in 1995 where he states that Don Macpherson came up with the name when he went out to instruct their first client of the new telephone system, the Mayo Clinic. He thought Bell Labs needed an unambiguous name for the # symbol, which had many names, so came up with “octothorpe”. The latter “thorpe” was in reference to the incredible Native American athlete “Jim Thorpe”, who at the time was trying to get his 1912 Olympic medals returned after having them stripped away due to the fact that he once had accepted money for playing a sport (baseball), previous to those Olympics. Macpherson at this time was part of the group that was trying to get Thorpe’s 1912 Olympic medals returned.

Douglas a Kerr of Bell Labs stated in 2006 that the term was invented by C Schaak and Herbert T Uthlaut and it was originally “octatherp”, which was more or less a joke term between the two. This seems less plausible than the previous story. Why would they say “octa” instead of “octo” and why would it have been changed relatively quickly after its creation to “octothorpe” in the first patent that references the term? Nevertheless, Kerr was there, so perhaps it’s true or perhaps not as Ralph Carlson was there too.

Given that the word circulated around Bell Labs for about 10 years before appearing in text, it’s also possible it was invented by Don Macpherson, as Ralph Carlson said, and that C Schaak and Herbert T Uthlaut mocked the term calling it “octatherp” as a joke, as Douglass Kerr said.

Bonus Facts:

Jim Thorpe eventually had his Olympic medals returned in 1983… 30 years after his death.

In the U.S. patent in 1973 where “octothorpe” first appears, the asterisk (*) was referred to as a “sextile”.

The # is often called the pound symbol in the United States as it is often used with numbers related to weight. Originally “lb.” was used for this same meaning. Later, printers designed a font containing a special symbol of “lb” with a line through the verticals so that the “l” wouldn’t be mistaken as a one (℔, Unicode character U+2114). Eventually, this changed to the more familiar and easier to type on a standard keyboard “#” symbol.

Another common name for the # symbol in the United States is “number”. In these two cases (pound and number), if the symbol precedes a number, as in #2, it is traditionally read as “number”. If the symbol follows the number, it is traditionally read as “pound”.

Yet another accepted name for the # symbol is “hash”, which is a popular one in the UK. It is also the generally accepted name for the symbol when referring to computer programming usage (often used as a comment sign, particularly in scripting languages).

An international standards body officially named the # symbol “square” in 1989. This is why the British Post Office and British Telecom call the symbol a square, instead of the more common British name for it of “hash”.

The # symbol is also commonly called a “sharp” in such places as Japan and others. In many places, this is as a result of the similarity to the musical sharp symbol (♯).

In Malaysia, the # symbol is commonly called a “hex”.

The * and # were originally selected to go on a standard telephone pad in 1961. Link Rice and Jack Soderberg at Bell Labs toured the country trying to find out what possible telephone/computer interactions might come up and what would be the best symbols to use for those. Eventually, they settled on the * and the # as those keys were available on standard typewriter keyboards.

In the U.S.-English layout of a standard keyboard, the # symbol appears on the same key as the number 3. On the UK-English keyboard, the character above the number 3 is the £. Americans call both of these symbols by the term “pound”, but the English never call “#” by “pound” for obvious reasons.

Microsoft’s programming language C♯ (pronounced C-sharp) is often mispronounced “C hash” or “C pound”. The confusion comes from the fact that the symbol following the C is supposed to be the musical sharp symbol (♯). But given the # symbols prevalence in various programming languages, most programmers assume it was meant to be the “hash” symbol, until corrected.

In scripting languages where a # is followed by a ! (as in #!), this is known as a “shabang” (sometimes spelled “sh-bang” or “shebang”) and is typically used to tell the operating system what program to use to run some script. The former name of “shabang” is thought to have come from the contractions “SHArp bang” or “haSH bang”; another popular theory is that it comes from the fact that the default shell “sh” is usually invoked with “shebang”, hence “sh-bang” and eventually “shabang”. The latter “bang” name for the exclamation point is traditional Unix jargon.

In Chess notation, the # symbol placed after a move indicates a checkmate. This replaced the more traditional ‡ symbol.

The compound tone generated on a phone by pressing the # key is a mixing of 941 Hz and 1477 Hz.

The two horizontal lines in the sharp symbol ♯ are optional in musical notation, but required in the # symbol.

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