Which programming language has the most return on investment? Impact on real world systems, and is more rewarding? I have minimal programming experience and working on AS in CS.

The formula says find maximum s such that 5*10^-s is greater than the relative error. But that gives me 4 as the answer. But it is visually clear that 3.122 is approximating 3.123 correctly only upto the first 3 significant digits. How is it possible? Is the formula wrong?

Is there a legitimate reason or is it just because people thought it looked better?