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 $A, CC$ curve shows consumption function whereas $45^{\circ}$ line represents income. $C$ curve intersects $45^{\circ}$ line at point $B$ at which $B R=O R$ i.e.,.consumption = income. Point $B$ is the break even point showing zero saving. It states that saving curve must intersect $X$-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 $B$ is positive saving.In part $B$, we derive saving function in the form of saving curve. In part $A$, the amount of saving is the vertical distance between $C$ curve and $45^{\circ}$ line. By plotting, the vertical distances of saving/dissaving and by joining them, we derive a saving curve. In part $A$ the vertical distance $O C$ (dissaving) is plotted as $\text{OS}_1$ below $X$-axis in part-B. At OR level of income in Part A, vertical distance at point $B$ is shown as point $B 1$ on $X$-axis in lower part of figure is nil. LM of part $A$ is shown as $L_1 M_1$ in part-B. By joining points $S, B_1$ and $L_1$ in lower segment, we get saving curve. Thus saving curve is derived from consumption curve.