  We investigate to which precision local magnification ratios, $\mathcal{J}$,
ratios of convergences, $f$, and reduced shears, $g = (g_{1}, g_{2})$, can be
determined model-independently for the five resolved multiple images of the
source at $z_\mathrm{s}=1.675$ in CL0024. We also determine if a comparison to
the respective results obtained by the parametric modelling program Lenstool
and by the non-parametric modelling program Grale can detect biases in the lens
models. For these model-based approaches we additionally analyse the influence
of the number and location of the constraints from multiple images on the local
lens properties determined at the positions of the five multiple images of the
source at $z_\mathrm{s}=1.675$. All approaches show high agreement on the local
values of $\mathcal{J}$, $f$, and $g$. We find that Lenstool obtains the
tightest confidence bounds even for convergences around one using constraints
from six multiple image systems, while the best Grale model is generated only
using constraints from all multiple images with resolved brightness features
and adding limited small-scale mass corrections. Yet, confidence bounds as
large as the values themselves can occur for convergences close to one in all
approaches. Our results are in agreement with previous findings, supporting the
light-traces-mass assumption and the merger hypothesis for CL0024. Comparing
the three different approaches allows to detect modelling biases. Given that
the lens properties remain approximately constant over the extension of the
image areas covered by the resolvable brightness features, the
model-independent approach determines the local lens properties to a comparable
precision but within less than a second. (shortened)
