There is plenty of information and instructions on tying a broken wound
string at the top (tuning pin) end. I found the missing piano string in
the bottom of an upright with the tuning pin coil still intact, but was
missing the hitch pin loop (loop was long gone, I looked). The problem
is trying to calculate the right length of new string at the hitch pin
end so the winding of the bi-chord string is close to it's neighbor at
the other (tuning pin) end and is clear of the bridge pins. I tried to
form a new hitch pin loop and tied a knot to the string, but my guess
was off by about a quarter inch (too long) and the knot ended up in the
middle of the bridge. I removed the string and left it at the bottom of
the piano for another day. Of course I could always order another
string for the nearly 50 year old Story and Clark, but was trying to
effect a less expensive solution.