When bends are involved you need to know how much to bend the note
up. This is indicated by writing a number after the 'b'.
For example, if you see this :
E----------------------------------------------------------------
B------7b9-------------------------------------------------------
G----------------------------------------------------------------
D----------------------------------------------------------------
A----------------------------------------------------------------
E----------------------------------------------------------------
it means strike the B string at the 7th fret, then bend the note up
two semitones (one whole step) so that it sounds the same pitch as
a note fretted at the 9th fret would do. (Sometimes the bend is
written with the second part in brackets, like this ---7b(9)--- )
Something like this :
E----------------------------------------------------------------
B------7b9--9r7--------------------------------------------------
G----------------------------------------------------------------
D----------------------------------------------------------------
A----------------------------------------------------------------
E----------------------------------------------------------------
means play the note at the 7th fret, bend up two semitones, strike the
note again whilst it is still bent, then release the bend so that the
note has it's normal pitch.
You sometimes get a note which is bent up only a quarter of a tone or so.
In this case it would look a bit strange to write :
B--------7b7.5--------
if you have to bend it up half a fret's worth.
Instead it's written as :
bend up 1/4 tone
E----------------------------------------------------------------
B------7b--------------------------------------------------------
G----------------------------------------------------------------
D----------------------------------------------------------------
A----------------------------------------------------------------
E----------------------------------------------------------------
with instructions on how much to bend written above the note.