To get equal sizes, you could use \DeclareMathSizes
in your preamble. The syntax is
\DeclareMathSizes{display size}{text size}{script size}{scriptscript size}.
You could simply set all to your default font size. In this example:
\documentclass[10pt]{article}
\begin{document}
\[
x = \frac{1}{x + \frac{1}{x + \frac{1}{x}}}
\]
\end{document}
where you firstly get different sizes:
![alt text](https://i.stack.imgur.com/YxnyH.png)
inserting this line
\DeclareMathSizes{10}{10}{10}{10}
changes the output to:
![alt text](https://i.stack.imgur.com/PEmBJ.png)
The Problem lies within the definition of \textsuperscript
that uses math mode.
\DeclareRobustCommand*\textsuperscript[1]{%
\@textsuperscript{\selectfont#1}}
\def\@textsuperscript#1{%
{\m@th\ensuremath{^{\mbox{\fontsize\sf@size\z@#1}}}}}
A possible workaround is redefining the actual command so that it will not get in the way with your equations, this needs graphicx
:
\renewcommand{\textsuperscript}[1]{\raisebox{0.8ex}{\scalebox{0.66}{#1}}}
Or this needs relsize
\renewcommand{\textsuperscript}[1]{\raisebox{0.8ex}{\smaller{#1}}}
I admit that this is just an easy workaround emulating the typrsetting of superscripts. It might be possible, that modern typography defines super/subscript in a certain way.
This also works with various enlargements of text sizes. This MWE also emulates a textsubscript:
\documentclass[12pt,oneside,letterpaper,titlepage]{article}
\DeclareMathSizes{12}{20}{14}{10}
%% Solution 1
\usepackage{relsize} %smaller
\renewcommand{\textsuperscript}[1]{\raisebox{0.8ex}{\smaller{#1}}}
\newcommand{\textsubscript}[1]{\raisebox{-0.4ex}{\smaller{#1}}}
%% Solution 2
%%\usepackage{graphicx} %scalebox
%%\renewcommand{\textsuperscript}[1]{\raisebox{0.8ex}{\scalebox{0.66}{#1}}}
%%\newcommand{\textsubscript}[1]{\raisebox{-0.4ex}{\scalebox{0.66}{#1}}}
\begin{document}
...modulation by Ca\textsuperscript{2+}...
...soluted in water H\textsubscript{2}O...\\
\tiny Ca\textsuperscript{2+}
\scriptsize Ca\textsuperscript{2+}
\footnotesize Ca\textsuperscript{2+}
\small Ca\textsuperscript{2+}
\normalsize Ca\textsuperscript{2+}
\large Ca\textsuperscript{2+}
\Large Ca\textsuperscript{2+}
\LARGE Ca\textsuperscript{2+}
\huge Ca\textsuperscript{2+}
\Huge Ca\textsuperscript{2+}
\normalsize
\begin{equation}
\sigma^2 = iI - \frac{I^2}{N}
\end{equation}
\end{document}
Further reading relsize and graphicx.
For chemistry typesetting (I guessed that on the calcium bit) there are some packages available, like bpchem or mhchem, that handle formulas quite well.
Best Answer
Try
dfrac
instead offrac
:You will need the
amsmath
package