The TBM_SETLINESIZE message sets the size of the line for a trackbar. The line size affects how much the slider moves for the TB_LINEUP and TB_LINEDOWN notification messages.
TBM_SETLINESIZE
wParam = 0;
lParam = (LONG) lLineSize;
Parameters
lLineSize
New line size.
Return Values
Returns a 32-bit value that specifies the previous line size.