Analog instrumentation is the use of analog signals (e.g. air pressure or electrical current) to represent changes within a system. Forming the basis of many measurement systems, analog instrumentation remains in use due to the simplicity, as well as the reliability of the systems.
ADI ADA4530 Femtoampere Input Bias Current Electrometer Amplifier
The ADA4530-1 is a femtoampere (10−15 A) level input bias
current operational amplifier suitable for use as an electrometer
that also includes an integrated guard ...