Piano tuning is an art and a science. The science comes in the form of physics. If you have ever tuned a guitar you know that when you tune one string (sharpen) the string next to that string changes (goes flat). On a guitar you have 6 strings. On a piano there are about 250 strings. So, imagine how difficult that process would be. And, then you needs to adjust the temperament. Basically, not all intervals are created equal. The thirds, fourths and fifths are slightly different in an equal temperament. The thirds are just a half of a beat wide or sharp and the fifths are about half a beat narrow or flat. This temperament is barely discernible. But, it is what gives the well tuned piano the best sound. It's what makes the difference between an electronic piano and acoustic piano.