The TBM_GETLINESIZE message retrieves 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_GETLINESIZE
wParam = 0;
lParam = 0;
Return Values
Returns a 32-bit value that specifies the size of a line for the trackbar.
Remarks
The default setting for the line size is 1.