First of all, ignore all other lines in the example chart except the four FAT lines. The four fat lines are the ones that define the fibonacci price leves. The lines have different extension offset to the right. The shortest one is the end of the second wave ( or leg B ), the next one is the end of C, the one following that is the end of D and the final one is the end of the final leg E.
The two input parameters is the start of A and the end of A.
If the start of A is larger than then end of A, the calculated series is a downward trend, else it is an upward trend.
Calculation based on old EWT simple wave expansion by fibonacci sequence. 0.618, 1.618, 0.382