  The paper analyzes the influence of the hole density, the out-of-plane or
in-plane disorder, and the isotopic oxygen mass on the zero temperature energy
gap ($2\Delta\left(0\right)$) for
$\rm{Y}_{1-x}\rm{Ca}_{x}\rm{Ba}_2\left(\rm{Cu}_{1-y}\rm{Zn}_{y}\right)_{3}\rm{O}_{7-\delta}$
(YCBCZO) and $\rm{La}_{1.96-x}\rm{Sr}_{x}\rm{Ho}_{0.04}\rm{CuO}_{4}$ (LSHCO)
superconductors. It has been found that the energy gap is visibly correlated
with the value of the pseudogap temperature ($T^{\star}$). On the other hand,
no correlation between $2\Delta\left(0\right)$ and the critical temperature
($T_{C}$) has been found. The above results mean that the value of the
dimensionless ratio $2\Delta\left(0\right)/k_{B}T_{C}$ can vary very strongly
together with the chemical composition, while the parameter
$2\Delta\left(0\right)/k_{B}T^{\star}$ does not change significantly. In the
paper, the analytical formula which binds the zero temperature energy gap and
the pseudogap temperature has been also presented.
