If a piano has gone without tuning for a long time, its pitch may have dropped far below A-440. This means that each of its approximately 220 strings needs to be tightened considerably, adding additional tension to the piano's structure. As each string is tightened, the additional load causes the pitch of previously adjusted strings to change. Thus it is impossible to make a substantial change in pitch and end up with a fine, accurate tuning in one step. So the piano needs to be tuned twice. The first “rough” tuning to get the piano close is called a pitch correction or pitch raise.
Also, the more the tension is changed on the strings the less stable the piano will be. So a piano that has gone through a pitch correction needs another tuning within a few months to get it to a stable “in-tune” state.
Some technicians charge extra for a pitch correction, which is usually less than half of the regular tuning charge. I can usually do the pitch raise and fine tuning in two hours and do not charge extra. I talk to the customer about doing another tuning within a few months to get it stable and remain in tune.