The sister chip to the 7106 is the 7107 which uses an LED display for its output.  There are two advantages to using the 7107 over the 7106.  The first is that because it is powered by +5V and -5V it can accept inputs in the range +4V to -4V. 

A second advantage is when a digital reading of zero is desired for a VIN not equal to zero as, for example, temperature and weighing systems with variable tare.  Both the offset voltage and the transducer voltage can be conveniently input directly to the 7107.  In 7106 systems null calibration requires additional electronics off-chip.

QK61 has been designed as a versatile 3 1/2 digit panel meter with these considerations in mind.

Also in this kit we have used small, monobloc capacitors rather than the much bigger mylar or metallized types. This saves space as well as making the meter look better. Some components are under the IC to save even more space.

Voltage is the most frequently measured electrical quantity. In meters to measure temperature, current, windspeed, resistance, lux, etc., what is actually being measured is voltage. After calibrating the meter for its particular purpose the voltage measured will give an accurate digital reading of the analog quantity being measured.

Digital displays have many advantages over analog meters which use a pointer and moving coil. Firstly, they are easier to read especially by unskilled labor. In the majority of applications it is better that the value displayed is exactly the value being measured, for example, 13.6V. To use an analog display with its many graduated scales (some going up and others going down) and switches requires considerable practice. But a simple LED display which reads '13.6' can be understood by everyone.

Second, DPM built using the 7107 are physically stronger and more robust than analog meters because they have no moving parts. 

Thirdly, for the manufacturer the assembly of the complete DPM unit can be done by relatively unskilled labor in third world countries.

Fourthly, the 7107 by its very nature can be adapted to so many uses at such a low cost that it has actually created markets for itself.  All of these factors add up to a better, cheaper product which everyone can afford.

The kit shows how much of electronics today can be contained in a single chip.  Commercial low to medium cost digital multimeters are nothing more than this kit, some switches and passive components and a plastic case.

The main reason today for the failure of meters is more likely due to switch contact and mechanical failure rather than failure of the electronics itself.

Two circuit boards have been used. The 4 LED displays mount on one board which is soldered to the mother board at right angles. This allows low profile end viewing.