In case the round pipes are of unequal diameter the order of triangulation is altered somewhat, but the general method of procedure remains the same. The true section on the miter line is developed by considering the fitting as a transition between the round pipe of larger diameter and the whole of the rectangular base. This section is used for the development of both pieces and the order would read:
| Order. | Proper Altitudes. | Spaces obtained from. | ||
| Triangles | K to 5 | True altitude of all triangles as shown in Fig. 301 | Circular profile in Fig. 301 | |
| 5 to M | True altitude of all triangles ss shown in Fig. 301 | Base Rectangle in Fig. 301 | ||
| M to 4 | True altitude of all triangles as shown in Fig. 302 | Circular profile in Fig. 301 | ||
| M to 3 | True altitude of all triangles as shown in Fig. 302 | Circular profile in Fig. 301 | ||
| 3 to E | True altitude of all triangles ss shown in Fig. 302 | Base Rectangle in Fig. 301 | ||
| Sections | 3 to D | True altitude and alt. of F, Fig. 303 | E to F in true section, Fig. 303 | |
| D to 2 | True altitude and alt. of F, Fig. 303 | 3 to 2 in true section, Fig. 301 | ||
| 2 to G | True altitude and alt. of G, Fig. 303 | F to G in true section, Fig. 303 | ||
| G to 1 | True altitude and alt. of G, Fig. 303 | 2 to 1 in true section, Fig. 301 | ||
| 1 to B | True altitude and alt. of H, Fig. 303 | G to H in true section, Fig. 301 | ||
| 1 to A | True altitude and alt. of H, Fig. 303 | H to A in true section, Fig. 301 | ||
It is required that the pattern be redeveloped according to the above order and the results compared with the first development.
92. Related Mathematics on Split Headers.—The question as to how large the branch pipes can or should be made often arises in fan or blower design. The following factors enter into the consideration of such questions :
(a) What percentage of the total volume available must be delivered in a given direction?
