The Obelus is a symbol that sounds like the title of a sci-fi movie, but it is used in Australia (and some other countries) to represent division. You will have seen it on your calculator, and used it many times. It looks like this, ÷ .
First introduced in 1659, the obelus has been steadily phased out because of its ambiguity. The organisation responsible for making a common standard for maths notation, The International Organisation for Standardisation (ISO), says the obelus is not to be used at all (see Reference 1). For the same reasons, the solidus represented by the symbol / also fails.
A viral maths problem that floats around from time to time is 6÷2(1+2). Everyone agrees this can be simplified to 6÷2(3), and everyone agrees this can be represented more generally by a÷b(c) or even a/bc. The ambiguity exists because there is no standard on how to approach this expression.
Some disciplines place precedence on what is known as multiplication by juxtaposition, which means that instead of writing b×c we write bc. After removing the multiply symbol the term bc is thought to have implicit multiplication aka multiplication by juxtaposition. Then, in older maths textbooks and certain disciplines such as engineering, the term bc takes precedence such that a/bc=a/(bc) while a/b×c = (a/b)×c. It is because of this ambiguity that both the obelus and the solidus have the potential to cause confusion without further use of brackets. Subsequently, Australian University level mathematics courses remove the ambiguity by solely using two line fractions.
However, if you look through the Australian Curriculum, you will still find the obelus (see Reference 2). Even though two line fractions solve all the issues, the syllabus explains how it is good to become familiar with different types of symbols. Today if you go to any primary school in Australia, you’ll see the obelus. If you go to any secondary school, you’ll still find the obelus in current textbooks.
So here’s my point. We introduce the obelus to school-aged students, and then once they reach university, we remove it! Is there anything else in maths like this? Not that I know of. But is it time to make the obelus obsolete? Probably not. I mean, isn’t this what we do with Santa Claus?
Reference 1: ISO 80000-2, Section 9 "Operations", 2-9.6
Reference 2: Retrieved from the world wide web 14/04/23, https://www.australiancurriculum.edu.au/media/7045/mathematics_all_elements_f-6.pdf p.72
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