# Central dot as decimal point in top journal

The Lancet, one of the top medical journals in the world, requires 'Type decimal points midline (ie, 23·4, not 23.4)'. Does anyone know why this is? As a mathematician, I'll always read 23·4 as 92. Seems odd to me that such a high profile paper would insist on such a strange formatting choice, which goes against the SI standard, so I'm guessing there's a good reason for it.

• Not really an answer, but there is precedent for use of a midline dot as a decimal point: en.wikipedia.org/wiki/Interpunct – anything Oct 5 '18 at 15:30
• When some of us hand write numbers with decimals (gasp! Pens & pencils still exist) we were taught to put the decimal point in the middle, as it could get “lost” when using lined paper... – Solar Mike Oct 5 '18 at 16:20
• FWIW when writing something by hand I would automatically put the decimal point midline (I'm British). But typing like this is too much effort - it's not on keyboards and even in LaTeX you would need to adjust the spacing. – Especially Lime Oct 5 '18 at 19:23
• I have only one paper in a British journal (Proceedings of the London Mathematical Society). Their copy-editor changed all the decimals in the paper. If I used 5.243, that was changed to 5･243 . – GEdgar Oct 5 '18 at 19:38
• @EspeciallyLime {\cdot} should work. Like, if you do 123 \cdot 4, then TeX'll put in extra spacing around it, but if you do 123{\cdot}4, it shouldn't. (Not that I recommend this; drives me nuts how various subcultures makes these little alterations, which just look plain silly to me.) – Nat Oct 6 '18 at 4:58

This notation was more common historically, particularly in the British empire. My guess would be that the Lancet, being an old journal founded in England in 1823, is sticking with it because of tradition rather than a really good reason.

• It would seem to me that tradition is a good reason. – MaxW Oct 7 '18 at 17:00
• @MaxW It's not a terrible reason on its own, and I'm not calling for an end to all traditions here, but if there are good reasons to stop or continue a practice, well, those reasons generally trump "we've always done it that way". Note that, for the purposes of this answer, I accept OP's premise that the notation is unusual and somewhat confusing. – Anyon Oct 7 '18 at 20:42

To expand on @Anyon's answer more generally, mathematical notation is not universal between countries. Where the decimal symbol appears—and what the decimal symbol even is—varies significantly. For instance, in most of continental Europe, the period and comma are switched so that what in the US would be "24,321.12" would be "24.321,12" in Germany or the Netherlands. Similarly, the "dot product" is sometimes written on the baseline rather than on the center line.

So this is just an expression of a stylistic preference or tradition.

• Sometimes the dot product is even written with a cross (and the cross product with a wedge). This confused me a hell of a lot in high school – Denis Nardin Oct 5 '18 at 16:17
• @DenisNardin and sometimes dot product is written with angle brackets like 〈a,b〉 – JAB Oct 5 '18 at 17:12
• In fact, modern scientific guides suggest to use a small space instead of a comma or a dot to separate thousands. – Massimo Ortolano Oct 5 '18 at 18:34
• @MassimoOrtolano This is the SI standard since 2003 to not use the comma or dot for anything but the decimal separator (bipm.org/en/CGPM/db/22/10) – LCT Oct 5 '18 at 18:45
• @JAB to add to the variation, in Russian literature dot product is commonly written as (a,b) (example), while cross product is [a,b] (example). And this despite comma being decimal separator. What a mess. – Ruslan Oct 7 '18 at 9:40

The unspaced centred dot, as in 23·4 (= 234 ÷ 10), means the decimal point. To denote multiplication, spacing is necessary: 23 · 4 = 92. As long as one sticks to this convention, no confusion arises. From some people's point of view, it is nice to distinguish thus the marker for decimal point from those for multiplication and the end of a sentence.

• This sounds like a very error-prone convention. – Eric Duminil Oct 8 '18 at 6:15
• I didn't downvote BTW. It's good to know this convention exists, even if it's a dangerous one. – Eric Duminil Oct 8 '18 at 9:57