Snap Cursor to Price
The Lock Cursor to Price feature will snap your cursor to the closest open, high, low, close, or midpoint of a price bar. This is useful when wanting to add manually-applied tools to your chart - such as a trendline or Fibonacci Retracement - to an exact value of a specific bar.
To toggle this option on and off, click the padlock icon on the Action bar on the far left of the screen, or use the keyboard shortcut CTRL+L.
When enabled a small ‘x’ will follow your cursor around the screen, and when placed near a bar/tool will show you where the tool will be applied: