# Vertical spacing between numerator and division symbol in \dfrac

How can I fix the vertical spacing between the numerator and the division symbol when entering fractions.

Eg. in the following code, the spacing between a and the division symbol is greater than one between b and the next (lower) division symbol.

$x = \dfrac{\dfrac{a}{b}}{c}$

-
First of all, stacking fractions is not a recommended practice. You can use \mathstrut in the denominator of the inner fraction, so it will be raised a bit. –  egreg Sep 16 '12 at 21:13
The a in the numerator is higher because you might have something like $\frac{a}{2}\frac{f}{4}$. –  egreg Sep 16 '12 at 21:49
@egreg I was trying to write $\phi = \frac{\dfrac{\text{fuel}}{\text{oxidizer}}} {\left(\dfrac{\text{fuel}}{\text{oxidizer}}\right)_{\text{st}}}$. I could so something like $\phi = \frac{\text{fuel}/\text{oxidizer}} {(\text{fuel}/\text{oxidizer})_{\text{st}}}$ but found the former one easier to read. Later on I try to substitute in the numbers which are in the (a/b)/c form. Also mathstrut worked $x = \dfrac{\dfrac{a}{\mathstrut{b}}}{c}$. –  mythealias Sep 16 '12 at 22:29
You might try to use \text{\raisebox{-.4ex}{fuel}} if you really like to reduce the vertical space. –  egreg Sep 16 '12 at 22:47
Following egreg's suggestion I found a document which talks about number of recommended practices. Others may find it useful. –  mythealias Sep 16 '12 at 22:57

\documentclass{article}
$x = \dfrac{\dfrac{a}{b}}{c} = \dfrac{\frac{\textstyle a}{\textstyle b}}{c} = \dfrac{\frac{a}{b}}{c} \equiv \dfrac{\tfrac{a}{b}}{c}$