Often one needs to show graphically relationship between four or more variables. Line nomographs with line scales (not grid) can tie together three variables. If more variables are to be shown one must use either grid nomographs, contour blocks or make compound nomograph.
Compound nomograph is nomograph that is constructed from blocks that each relate variables with a single line. In practice this means splitting a single equation to many equations, each having variables for one block. In the following Fig. is illustrated the basic idea:
Two blocks are defined and a 'tag' is defined to align proper scales with each other.