Harmonica : what is a bend -4''?

https://www.harptabs.com/song.php?ID=16307

Does it exists ? -4' is Db so -4'' is C, +4 in fact ?

Btw, replacing -4'' by +4 sounds right.

What have I missed ?

• I don't really know much about harmonica, but playing a straight C and bending a D down to C will sound quite different; my guess is that the sound of a bent note is what is desired here. – ex nihilo May 2 '18 at 1:12

That is explained in the tab guide (section 3), but a negative hole number typically stands for a draw note, and each single-quote next to it means a half-step bend, so -4" would be draw 4, bent two half-steps... which is a broken notation because draw 4 doesn't go any lower than C# (Db) on a C harmonica.

Btw, replacing -4'' by +4 sounds right.

4" looks like a tabbing error; two half-steps down from D is indeed C.

Rule of thumb, follow your ears - tabs tell you roughly where it's at, but tabs can have errors (you may want to contact the author and see if they want to fix it), and don't (can't) tell you everything about every note.