To fine-tune the frequency, use the arrow keys on your keyboard (works only if the slider has focus) or use the control shown in the figure above. The frequency steps available depend on the selected block size. If you increase the block size, the frequency steps become finer but updating becomes slower.
You may also type the desired frequency directly in the edit box shown in the figure above. If the current WinMLS setting does not support the frequency, the nearest supported frequency will be displayed when the edit box looses focus (to have it loose focus pus the Tab key or click somewhere else with the mouse).