The reason for starting this project was found in a shoebox :-)

Finally, I found my lost Kyoritsu DMM KEW1012 in a old shoe box.

Now after almost one year of research and all the knowledge, which I collected about the measurements, I have feeling that this DMM is like a toy. His basic DC accuracy is ±0.5% ±2 digits and the input impedance is 10MOhms for the useful ranges.

Even if my calculations for the first voltmeter prototype are 10 times worst, it will be still 50 times better then the specification of the KEW 1012 DMM. 

Nevertheless, I can still use this DMM for the high voltage ranges and for the frequency and duty cycle measurements. So, I will not throws it in the bin for sure :-).