While correcting a thesis of a colleague I found this:
As you can see, the parentheses around the first and the second item differ, however, they're implemented in the exact same manner (see code snippet and highlighted source code respectively).
\begin{equation} \left( p+\frac{a\rho ^2}{N^2_{A}} \right) \left(1-\frac{\rho}{N_{a}}b \right) = \frac{\rho}{N_{a}}R\vartheta \end{equation} Can anyone explain how they come to look different? Is it because of the indices and exponents?
TeX fonts have a certain number of delimiters in a range of sizes, and then at some point they switch to a scheme that uses a repeatable straight section to make delimiters of arbitrary size. You just happened to hit the tipping point where one delimiter is a fraction over the point at which it switches to the extendable section. Different font sets will switch at different points, depending how many designed delimiter sizes the font has.
\bigl(....\bigr) with l and r but yes choosing a size manually is probably the easiest thing here (and often improves the horizontal spacing anyway)
amsmathpackage, I can't confirm the difference between the parentheses. We need more informationamsmathandamssymbis used here and the standard classscrreprt. Font packagekpfonts.kpfontspresumably being the decisive information, that's why it's always best to post a complete (small) document that demonstrates the effect, rather than a fragment which may or may not depending on what other code is needed.