% A callout anchored to a face rather than to a band: the card lands beside a
% single operand and reads as a step in the computation.
\documentclass{standalone}
\usepackage[en]{supertensor}
\stdim{T}{4}
\begin{document}\begin{tikzpicture}
  \strow{R1}{T}
    \stface{A}{}{T}{T}
  \strowend
  \stcallout{N1}{3cm}{A}{aside}{anchored to a face, not to the band}
  \sttopformula{F}{$A$}
\end{tikzpicture}\end{document}