What is a pitch raise, and why is it necessary?
When a piano has not been regularly maintained, it often drifts very far from its target pitch center. Most pianos are manufactured to perform optimally at A440: with the note A4 being tuned to 440hz and everything else tuned to that.
When a piano has been neglected for a number of years, it's not uncommon for it to be as much as 100-200 cents flat - 100 cents being the distance between two notes on a piano. In other words, a piano that is 100 cents flat sounds a B when you play an C. This is a problem for many practical reasons, but the most basic is that the piano is designed to work and sound best at a certain level of tension on the strings, and anything significantly less is compromising the performance of the instrument.
The other fact that many piano owners do not realize is that pianos do not go uniformly out of tune. As you can see...