Hi Andy
There are two preference settings: X (and Y) Axis Grid Opacity. They are set at 0 by default, but you can set them to any value, depending on how strong you want the lines to appear. The X axis grid will show vertical lines for every 5 minutes. The Y axis grid will divide the curve level into fifths, and show horizontal lines for each level.
You can alter the "Max Graph Temp" preference setting to adjust where the horizontal lines fall. For example, changing that from the default of 260°C to 270°C is a good choice. That will make the top two lines represent 216 and 162, and serve as good reference guideline for when you should start to watch for 1st and 2nd crack.
Hope this helps.