Let's consider an extreme example. Say you have a 36" header with a 2" branch. Furthermore, assume the branch pipe runs for 6" to an elbow.

CAESAR II models the system using beam elements, which span between two nodes. If you simply model this intersection between two nodes, the length of the 2" line is really 24" (18 inside the header plus the actual 6). While this may be geometrically correct, it is incorrect from a stiffness point of view.

One way to avoid this error is to use offsets to correct the length of the branch element. There are examples on the use of offsets in the Technical Reference Manual.