The Graph Settings tab of the Format Graph dialog

Gaps at missing points.

Leave a gap when you have missing data points, or connect the existing data points on each side.

Reset any individual formatting of points or bars

If you have changed the format of individual data points (by right clicking on them) , check an option here to reset everything back to the format set in the dialog.

Line of identity

The line of identity is a line where every value of X exactly equals Y. If the X and Y ranges are the same, it is a 45 degree line. It is created automatically by some analyses, and you can check this option to add to any XY graph. If you want this line to show when the file is opened with Prism 7 or earlier, there are other ways to create it.