This Circuit is a DPM or digital panel meter. It has a analog bar graph display and a 3-1/2 digit digital display. ICL7107 is used in the 200mV configuration.
U4A opamp LF353 amplifies the 200mV Full scale input to the level required for the LM3914 display circuit. D13-D14 are clamping protection diodes. Adjust P1 trimpot for a reading of 1000 counts when a 100.0 mV signal is fed at Vin. Adjust R8 trimpot to get the 5th led to just turn on at 100mV input.
Analog and Digital Voltmeter using ICL7107
A combination of digital and analog display is helpful for quick decision making. Analog indicates even from a distance the process dimension.
Human Brain understands analog better. The digital is required to note down and record values for determining a setpoint or performance of a system.
Sometimes a analog recorder with a ink-pen plot against time is a very good way of process analysis. Many systems are better studied using graphs not tables and lists of numbers. A Computer based data-logger gives greater power to this methods. You can measure and plot graphs of various types and at different points and for much longer periods.
This is a part of my Build a DMM or Digital Multi Meter