A PIC-chip microprocessor is used to send data down a serial cable into the Newton which will function as an oscilloscope, a chart-recorder, or a digital-meter.
fleXYlog.pkg for the Newton is available here: downloads page
These examples Case-Study 1 Case-Study 2 illustrate fleXYlog in use.
The fleXYlog zip file contains a 48-page manual - also provided here for viewing on-screen: fleXYlog.pdf
Sample image of fleXYlog's chart-recorder capturing some frequency data: