In my life¹, I have never seen a symbol other than ≈ used in handwriting to express “approximately equal”. The symbol ~ was only used for more mathematical purposes such as equivalence, proportionality, or “is distributed as”. Yet, I often see the symbol ~ used for “approximately equal” in the scientific literature, in particular in fields where TeX use is scarce.
I do not want to debate what is right™ here, but I am just curious whether this usage is a result of the limitations of typewriters and predominant keyboard layouts and encodings from the early days of computing, which make ≈ difficult to produce or impossible to encode, while ~ is readily available.
By contrast, I would expect that in moveable type (and similar systems that do not allow superimposing characters), you either had both or neither glyphs available, as I am not aware of any relevant application for the ~ glyph besides equations in such systems².
Also, in TeX, both symbols are comparably difficult to use (
Is there any harder evidence that the usage of ~ for “approximately equal” is a consequence of it being a makeshift solution in light of technical restrictions? For example:
- Examples of ~ being used for this purpose in systems that do not technically favour this symbol.
- Works of the same author using ~ only when technical restrictions applied.
- Historical guidelines on symbol usage.
¹ I went to school and studied physics and math in Germany.
² On a typewriter, the ~ character could be superimposed with, e.g., n to obtain ñ.