snapping to an (invisible) grid is done internally by rounding.

compare these three pieces of code:

(

var w;
w = SCWindow("snapping", Rect(128, 64, 380, 190));
b = SCSlider(w, Rect(10,10, 330, 50));
c = SCSlider(w, Rect(10,90, 330, 50));

c.action = { b.step = c.value };
w.front; 

)

(

var w;
w = SCWindow("snapping", Rect(128, 64, 380, 190));
b = SCSlider(w, Rect(10,10, 330, 50));
c = SCSlider(w, Rect(10,90, 330, 50));

b.action = { b.value = b.value.round(c.value) };
w.front; 

)

(

var w, d;
w = SCWindow("snapping", Rect(128, 64, 380, 190));
b = SCSlider(w, Rect(10,10, 330, 50));
c = SCSlider(w, Rect(10,90, 330, 50));

d = ControlSpec(0, 1);

b.action = { b.value = d.map(b.value) };
c.action = { d.step = c.value };
w.front; 

)