Underbrace space without underbrace?

Question

I want to diagram what 4 KB means.

$\underbrace{4}_{2^2} \underbrace{\text{KB}}_{2^{10}}$

I'd like to put a multiplication sign between the two underbrace in the underbrace space (same level, size, etc) without the multiplication sign actually having a brace over it. And maybe even an = 2^{12} part at the end in the same style.

Answer 1

Something like this?

The \mkern2mu directive inside the argument of \mathllap serves to places the \times symbol right below the gap between the two horizontal braces. (A larger value for the argument of \mathllap would push the \times symbol further to the left.) Likewise, \mathrlap{\cramped{\,=\,2^{12}}} serves to place =2^{12} to the right of the main argument of the second \underbrace directive.

\documentclass{article}
\usepackage{mathtools} % for '\mathllap', '\mathrlap', and '\cramped' macros

\begin{document}
\[
\underbrace{4}_{2^2} 
\underbrace{\mathrm{KB}}%
    _{\mathllap{\times\mkern2mu} 
      2^{10} % <-- main argument of '\underbrace'
      \mathrlap{\cramped{\,=\,2^{12}}}}
\]
\end{document}