The number relates to the slat position that you get according to flap lever position. Which is not very intuitive I am afraid.
I am pretty sure the old QRH had only four boxes down the side whch you could directly equate to each dot.
The way I look at it is :
S=0 slat position at 0 dot.
0<S<1 slat posn greater than 0 dot but less than 1st dot
S=1 slat posn at 1st dot.
1<S<=3 slat posn greater than 1st dot but less than or equal 2nd dot. This is because slat positin does not change from flap 2 to flap 3.
S>3 slat posn greater than 2nd dot.