This was designed, keeping in mind, that sometimes we have few components available and you could not carry your DMM somewhere, but you have to make some instrument for a quick need with what is available.
Analog Dial AVO Amps-Volts-Ohms meter
IC3 LM555 is to generate -5V from 9V. That reminds me of a story, I came across a Book called CMOS Hot Ideas of Intersil. I had a chance to observe, build and learn some things here. The ICL7107 circuit was the most fascinating, I also read the books of National Semiconductor at that time.
In those days small firms used to make DPM's digital panel meters with 7107. In 1987 when i got a oppurtunity to design a DPM for a firm, I put the 555 clock in place CD4009 clock shown in intersil, to derive the -5.
Many times we cannot carry big or expensive test instruments to the field, so we have to have a troubleshooting tool kit. Continuity testers, Logic Probes, DMM, Clamp Meters etc.. You can troubleshoot and repair Electronic Equipment easily with Meters and Continuity Tester.
Small Electronic Testing Tools - Analog Dial AVO Amps-Volts-Ohms meter
Potentiometer Dial GIF for above circuit to be used to make a hand-held avo-meter is here.
It also is sometimes required to build a quick jig or fixture with electronics to troubleshoot, simulate a problem or to test the reliability or aging of components and systems. Here you need to be cost effective, fast and innovative; and build a simple system with available, affordable or procurable resources. Hence a bit of circuit design, firmware and software are essential skills for production engineering.