davekw7x - Well if for example on the LCD i see 1.76V, then on the other row i need to see: y = 4621.2x - 281.96; i.e. 7851.32 (calculation).

But it doesnt give me this number.

No, it doesn't give you that number, and I would not expect it to.

Have you looked (yes

*looked*) at the calculations in the program?

Well, without knowing what your real expectations from the program are, and without worrying about whether the program correctly implements what it needs to do to meet your expectations, and without caring about

*why* it has been written the way that it was to do what it does, I'll step away from the Arduino for a minute, and I will go through the calculations that the program actually performs, but I will do them with my 10-digit calculator. (See Footnote.)

The calculation in the program gives, approximately, the (truncated) integer value of (1.76*4621.1-281.96-326+50), so I would expect to see something "in the neighborhood of" 7575 on the second line of the LCD.

In fact, if the number shown on the first line of the LCD is 1.76, it represents a number that was rounded to two significant digits, so the actual value could be anything between 1.755 and 1.765. Repeat the actual calculation with these numbers, and you can see that value on the second row could be anything from 7552 to 7598.

Regards,

Dave

Footnote:The floating point calculations in the Arduino are carried out with a precision of something like six or seven significant decimal digits. For this particular formula, roundoff error does not alter the results significantly, so I would expect the same output on the LCD that I show above for my calculator.