  We point out that testing the equality of the Cabibbo angle as extracted from
$\Gamma(K\rightarrow \pi l\nu)$, the ratio $\Gamma(K\rightarrow
l\nu)/\Gamma(\pi\rightarrow l\nu)$ and nuclear $\beta$ decays is not identical
to a test of first row unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix.
The reason is that a CKM unitarity test involves only two parameters, while the
degrees of freedom for the assessment of the goodness-of-fit of the
universality of the Cabibbo angle entailed by the Standard Model (SM) is equal
to the number of measurements minus one. Beyond the SM all different processes
could in principle give different Cabibbo angles. Consequently, the difference
between the two tests becomes relevant starting from three observables giving
results for the Cabibbo angle that are in tension with each other. With current
data, depending on the treatment of the nuclear $\beta$ decays, we find that
New Physics is favored over the SM at $5.1\,\sigma$ or $3.6\,\sigma$ while CKM
unitarity is rejected at $4.8\sigma$ or $3.0\sigma$, respectively. We argue
that the best method to test the SM is to test the equality of the Cabibbo
angle, because CKM unitarity is only one aspect of the SM.
