The standard potentials of ${\mathrm{Cu}}^{2+}\mid \mathrm{Cu}\text{ and }{\mathrm{Cu}}^{+}\mid \mathrm{Cu}\text{ are }0.337\mathrm{V}\text{ and }0.521\mathrm{V}$ respectively. The standard potential of ${\mathrm{Cu}}^{2+},{\mathrm{Cu}}^{+}\mid \mathrm{Pt}$ half cell is

$\begin{array}{l}{\mathrm{Cu}}^{2+}+2{\mathrm{e}}^{-}\to \mathrm{Cu}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\mathrm{\Delta }{G}_1^{\circ }=-2F\left(0.337\mathrm{V}\right)\\ {\mathrm{Cu}}^{+}+{\mathrm{e}}^{-}\to \mathrm{Cu}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\mathrm{\Delta }{G}_2^{\circ }=-F\left(0.521\mathrm{V}\right)\\ {\mathrm{Cu}}^{2+}+{\mathrm{e}}^{-}\to {\mathrm{Cu}}^{+}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\hspace{0.25em}\mathrm{\Delta }{G}_3^{\circ }=\mathrm{\Delta }{G}_1^{\circ }-\mathrm{\Delta }{G}_2^{\circ }=-F(0.674\mathrm{V}-0.521\mathrm{V})=-F\left(0.153\mathrm{V}\right)\end{array}$Hence $E^{\circ }\left({\mathrm{Cu}}^{+}\mid \mathrm{Cu}\right)=0.153\mathrm{V}$