The Keithley 485 is a dedicated Picoamperemeter from the mid-1980s, from the same generation and model series as the better-known 197 "Microvolt DMM".
The 485 operates as a feedback (transimpedance) amperemeter (i.e. the input burden is constantly low at less than 0.2 mV), has a resulution of 4½ digits (19999) and some rudimentary built-in logging capabilities as well as an optional GPIB interface.
This instrument measures only (low) currents, in seven decadic ranges from 2 nA to 2 mA full scale. Of course, marketing logic makes a meter with a lowet range of 2 A a picoamperemeter because the rightmost digit does resolve 100 fA (0.1 pA) ...
In a related article, I'm investigating how true the claim to the picoampere actually is. Surprisingly, ... no, sorry, no spoilers.