A standard piano has over 200 strings, each under approximately 160–180 pounds of tension, for a combined total of nearly 20 tons of string tension. Most notes use two or three strings tuned precisely together (called unison tuning). When these strings drift apart—even slightly—the note can sound thin, unstable, or harsh.
In some cases, a piano may have dropped significantly below standard pitch due to long periods without service or extended exposure to dry conditions. In these situations, a pitch raise is required before fine tuning can take place.

