  The introduction of the Rossby number (R$_0$), which incorporates the
convective turnover time ($\tau$), in 1984 was a pioneering idea for
understanding the correlation between stellar rotation and activity. The
convective turnover time, which cannot be measured directly, is often inferred
using existing $\tau$-mass or $\tau$-color relations, typically established
based on an ensemble of different types of stars by assuming that $\tau$ is a
function of mass. In this work, we use {\it Gaia} Early Data Release 3 to
demonstrate that the masses used to establish one of the most cited $\tau$-mass
relations are overestimated for G type dwarfs and significantly underestimated
for late M dwarfs, offsets that affect studies using this $\tau$-mass relation
to draw conclusions. We discuss the challenges of creating such relations then
and now. In the era of {\it Gaia} and other large datasets, stars used to
establish these relations require characterization in a multi-dimensional
space, rather than via the single-characteristic relations of the past. We
propose that new multi-dimensional relations should be established based on
updated theoretical models and all available stellar parameters for different
interior structures from a set of carefully vetted single stars, so that the
convective turnover time can be estimated more accurately.
