Consumption + saving is always equal to income because income is either consumed or saved. It implies that consumption and saving curves representing consumption and saving functions are complementary curves.
In part $\mathrm{A},\mathrm{CC}$ curve shows consumption function whereas ${45}^{\circ }$ line represents income. $\mathrm{C}$ curve intersects ${45}^{\circ }$ line at point $\mathit{B}$ at which $\mathit{B}\mathit{R}=\mathit{O}\mathit{R}$ i.e.,.consumption = income. Point $\mathrm{B}$ is the break even point showing zero saving. It states that saving curve must intersect $\mathrm{X}$-axis at the same income level where consumption curve and ${45}^{\circ }$ line intersects. Left of point B is negative saving and to the right of point $\mathit{B}$ is positive saving.
In part $\mathit{B}$, we derive saving function in the form of saving curve. In part $\mathit{A}$, the amount of saving is the vertical distance between $\mathit{C}$ curve and ${45}^{\circ }$ line. By plotting, the vertical distances of saving/dissaving and by joining them, we derive a saving curve. In part $\mathrm{A}$ the vertical distance $\mathit{O}\mathit{C}$ (dissaving) is plotted as ${\mathrm{OS}}_1$ below $\mathrm{X}$-axis in part-B. At OR level of income in Part A, vertical distance at point $\mathit{B}$ is shown as point $\mathit{B}1$ on $\mathit{X}$-axis in lower part of figure is nil. LM of part $\mathit{A}$ is shown as ${\mathrm{L}}_1{\mathrm{M}}_1$ in part-B. By joining points $\mathit{S},{\mathit{B}}_1$ and ${\mathrm{L}}_1$ in lower segment, we get saving curve. Thus saving curve is derived from consumption curve.