The following figure, is the consumption curve. The $45^{\circ}$ line is the aggregate supply curve. At point A, consumption = income i.e., $(Y=C)$ represents the autonomous consumption i.e., consumption at zero level of income. Steps for derivation of supply curve from consumption curve is as follows : (i) Corresponding to in the consumption function we have-in the saving function. That is, there are negative savings equal to autonomous consumption at $Y=0$. This is represented by $S$ on the negative axis in the lower panel. (ii) At point $A(Y=C)$. This implies that all the income is spent on consumption expenditure. Thus savings equal to zero. This is shown as $S$ $=0$ in lower panel. This point is also known as the Break-even point. (iii) Beyond the break-even point, by connecting points $S$ and $B$ we derive the straight upward sloping saving curve. (iv) $SS$ is the required saving curve.