  The stability of an approximating sequence $(A_n)$ for an operator $A$
usually requires, besides invertibility of $A$, the invertibility of further
operators, say $B, C, \dots$, that are well-associated to the sequence $(A_n)$.
We study this set, $\{A,B,C,\dots\}$, of so-called stability indicators of
$(A_n)$ and connect it to the asymptotics of $\|A_n\|$, $\|A_n^{-1}\|$ and
$\kappa(A_n)=\|A_n\|\|A_n^{-1}\|$ as well as to spectral pollution by showing
that $\limsup {\rm Spec}_\varepsilon A_n= {\rm Spec}_\varepsilon A\cup{\rm
Spec}_\varepsilon B\cup{\rm Spec}_\varepsilon C\cup\dots$. We further specify,
for each of $\|A_n\|$, $\|A_n^{-1}\|$, $\kappa(A_n)$ and ${\rm
Spec}_\varepsilon A_n$, under which conditions even convergence applies.

Numerical Analysis;Numerical Analysis;Functional Analysis;Spectral Theory