What are multiple axes in graphs?

An arrangement of axes (coordinate scales) in graphs, where two or more axes are placed parallel to each other in order to either:

• represent different units in which the variable(s) depicted in the graph can be measured (e.g., Celsius and Fahrenheit scales of temperature), or

• allow for a comparison of trends or shapes between several plots placed in one graph (e.g., one axis for each plot) which otherwise would be obscured by incompatible measurement units or ranges of values for each variable (that is an extension of the common "double-Y" type of graph).

The latter instance, which requires the appropriate plot legends to be attached to each axis, is illustrated in the graph above.