Bode plotter
An electronic instrument, named after Hendrik Wade Bode, an American Engineer and Academic, resembling an oscilloscope, which produces a Bode diagram, or a graph, of a circuit's voltage gain or phase shift plotted against frequency in a feedback control system or a filter. It is extremely useful for analyzing and testing filters and the stability of feedback control systems, through the measurement of corner (cutoff) frequencies and Gain and Phase Margins.
This is identical to the function performed by a vector network analyzer, but the network analyzer is typically used at much higher frequencies.