A modular probe assembly for a signal processing instrument has an elongate member extending from a first module of the probe assembly and a cavity recessed in a second module of the probe assembly. The cavity of the second module is structured to receive the elongate member of the first module. A module for the probe assembly may have a first articulating elongate member disposed at an end of a housing of the module. The elongate member extending from a first module of the probe assembly may be inserted into a cavity recessed in a second module, and the first module may be removably joined to the second module.