When a piano goes without tuning for an extended period, its pitch may have dropped far below A-440. This means that each of the 220 strings in the piano needs to be tightened considerably, adding tremendous additional tension to the piano’s structure.
The problem arises as each string is tightened, the additional load causes the pitch of previously adjusted strings to change in tension. Hence, its impossible to achieve a fine, accurate tuning in one step, when a substantial change in pitch is to be made.
This is why a process called ‘pitch raise’ must first be done, in which all the strings are tensed to their correct average tension levels. Only after this first step, can the piano be accurately tuned in the second step to A-440.
Hence, the next time your piano tuner does a pitch raise, he is having to tune your whole piano twice in one visit, which means double the work when compared to a normal tuning.