The strings of a harp are named, in an ascending sequence (longer to shorter strings):
A B C D E F G. This repeats as the strings move upward: A B C D E F G A B C D E F G, etc.
The number and range of strings varies widely as does the name of the lowest and highest string on any particular harp. Smaller harps have fewer strings. Larger harps have more. But all use the same sequence of string names, and the same color coding.
The C's are red, the F's are black (sometimes blue or dark purple).
In - between strings are neutral in color.
A is two strings below C, hence A, then B, then C etc. in ascending sequence
F is three strings above C, hence C then D then E then F
The RANGE of strings refers to the groups (FGABCDE) that are higher or lower.
A few builders identify string range by counting DOWNWARD from the top most string.
But MOST builders identify string range by OCTAVE.
An OCTAVE consists of 7 strings from an E moving DOWNWARD to the next F.
The TOPMOST F and any strings ABOVE it are considered to be FIRST OCTAVE strings.
Some harps have only 2 or 3 strings above the topmost F.
Others go all the way up to E in which case there is now a full FIRST OCTAVE.
E1 D1 C1 B1 A1 G1 F1 (topmost F)
*** Exception: Concert grand harps have an additional two strings at the top that are ABOVE FIRST OCTAVE and are sometimes named 00F and 00G.
Below the topmost F (F1):
The seven strings moving DOWNWARD from E2 to the next F2 constitute the second octave.
The seven strings moving DOWNWARD from E3 to the next F3, constitute the third octave.
The seven strings moving DOWNWARD from E4 to the next F4, constitute the fourth octave.
----and so on.
MIDDLE C resides in the 4th octave of both lever and pedal harps.
Smaller harps have many fewer low strings because they require a great deal of tension that smaller frames cannot support.
Low strings on a harp are made of different materials (wire, wound wire, etc.) and may have different color coding, e.g. bronze vs. silver color. This varies greatly from builder to builder.
ASK YOUR DEALER - BUILDER - OR TEACHER TO SPECIFY THE RANGE OF YOUR HARP