Page:Sheet Metal Drafting.djvu/160

146 of the body size, in order to obtain the free area of the register. Fill in, in the following table, the free areas of the register sizes given.

Problem 34C.—Since a register cannot deliver more air than is conveyed to it, it is evident that the cross-sectional area of the round neck of the register box must equal the free area of the register. Using the formula, $$\scriptstyle{D=\sqrt{\text{Free area}\div.7854}}$$, fill in the third column of the above table.