In drawing a flow net the beginner will make considerable use of the eraser, but with some practice a net can be sketched with fair facility to represent any boundary configuration. It is possible to construct an approximate flow net for cases where one solid boundary does not exist and the fluid extends laterally indefinitely, as in the flow around an immersed object. Such a case reveals an advantage of the flow net that is not evident form Fig. 3.9. In the flow between confining solid boundaries it is always possible to determine the mean velocity across any section by dividing the total flow by the section area. For floe around an immersed object, as in Fig. 3.11, there is no fixed area by which to divide a definite flow, but the flow net affords of determining the velocity in the region of such an object.