I uploaded the A3 firmware iteration. 

I'm sorry it contains some comments that are not in English. I will modify this for further variants. 

At this stage, the software contains only two of the intended four menus. In case you are wondering which tool am I using for programming the MSP430G2553, it is IAR embedded workbench. I tried Code composer, but I like IAR better. 

I'm facing a problem, though: I have a low cost free licence which limits the code size to 8K. This code that I uploaded, has already more than 6K and I need to implement the other menus too. It is true that my code is not optimized yet, but I still face this challenge. If you have some ideas or advises about any other IAR cheap licence I could purchase, or if you know some other programming environment that allows me to use the maximum MCU memory, please message me.    

I played a lot with the voltage divider resistor values and with the op-amp resistors, so if you find something that it's out of it's place in the mathematical formulas for calculating these values, please excuse me. 

Stand by for updates.