From: hees@fias.uni-frankfurt.de   
      
   These are great journals since they care for century-old good practice   
   in microtypography.   
      
   The rules are that mathematical constants like i, e, pi etc. are set   
   upright. The same holds for operators like the differential d. All units   
   have to be set upright.  Physical constants (even those which are   
   exactly defined in the new SI like c, h, \hbar, etc.) however have to be   
   set in italics. The Newton gravitational constant is also to be set in   
   italics (it's not even a fixed value in the SI for understandable   
   reasons).   
      
   All variable quantities are set in italics. The only exception are   
   capital greek letters (in the German and the Anglo-Saxxon tradition; the   
   French also set these letters in italics). The same holds for indices,   
   which are variable (e.g., running over 1 to 3 in 3D in Euclidean or from   
   0 to 3 in Minkowski/GR vector calculus). In contradistinction to that if   
   the index is a descriptor like $k_{\text{B}}$, where the B stands for   
   Boltzmann and is not variable, it should be set upright.   
      
   In LaTeX there are extra packages for a full upright Greek math   
   alphabeth (it's also included in the exceptionally good font package   
   mathdesign, where you have the choice full math alphabeths in very nice   
   fonts like Garamond, Utopia, Charter).   
      
   On 26/04/2020 11:23, Phillip Helbig (undress to reply) wrote:   
   > Some journals require upright Greek letters for constants as opposed to=20   
   > variables, for example $\upi$ when used to denote 3.14159... as opposed=20   
   > to a variable ($\pi$ is sometimes used to denote parallax in astronomy,=20   
   > for instance).  (Some journals define \upi as "upright pi", \upi as=20   
   > "upright i", and so on.)   
   >   
   > I certainly agree that LABELS should be upright (though they are usually   
   > Latin not Greek) and not italic to distinguish them from variables, e.g.   
   > $T_{mathrm{eff}}$ for effective temperature or $\rho_{textrm{g}}$ for   
   > gas density, say, as opposed to $G_{\mu\nu}$ where $\mu$ and $\nu$ are   
   > not constants but variables.=20   
   >   
   > And it is not just Greek letters.  For example, e for the Euler number=20   
   > or i for the square root of -1 should also not be in math italic, to=20   
   > distinguish them from variables.  I tend to agree with that as well. =20   
   > Also, units should be upright, e.g. 5 m and not $5m$ for 5 metres.   
   >   
   > On the other hand, I have never seen the gravitational constant $G$,=20   
   > which is even by definition a constant and not a variable, written=20   
   > upright.  Ditto for the Hubble constant $H$ and so on.=20   
   >   
   > Or is there a difference between mathematical constants and physical=20   
   > constants?   
   >   
   > Perhaps because standard (La)TeX provides Greek letters only in math=20   
   > italic, upright Greek letters are less common than upright Latin=20   
   > letters, even when used in the same way (labels, units, symbols which=20   
   > are not variables).   
   >   
   > When writing for a specific journal, one usually has to follow the house=20   
   > style.  However, if there is no rule, I prefer to do what is generally=20   
   > deemed to be correct.  What is generally deemed to be correct here? =20   
   >   
      
      
   --   
   Hendrik van Hees   
   Goethe University (Institute for Theoretical Physics)   
   D-60438 Frankfurt am Main   
   http://fias.uni-frankfurt.de/~hees/   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)