The core apparatus for measuring cardiovascular activity, respiration, and GSR remained fundamentally unchanged since whose era?

Answer

Keeler’s era

Many sources agree that the hardware for monitoring the traditional three core channels—cardiovascular activity, respiration, and GSR—has remained fundamentally unchanged since Leonarde Keeler's era, when he added GSR to the device in 1939.

The core apparatus for measuring cardiovascular activity, respiration, and GSR remained fundamentally unchanged since whose era?
inventionHistorytechnologycomputerpolygraph