You will notice that many of our string charts list note names followed by a number. For example, we say the range of our Jolie Harp is C2 to G6. What, exactly, does that mean?
When we say that a harp starts on the note C, we need some way to communicate which C we mean. We have adopted the use of Scientific Pitch Notation (SPN). SPN is a way to identify a specific musical pitch using the musical note name and a number which identifies the pitch’s octave.
In this system, Middle C on a piano is C4. The number, or octave, changes on the C notes. So the C one octave above middle C would be C5 and so on. A440 = A4
This diagram of a piano keyboard shows how this works.
Here are some common instruments and their tuning labeled with SPN: