I want to delete the ruler (erase the purple lines from the canvas)
When you create a ruler, a purple line is displayed on the canvas.
The ruler can be deleted, and display/hide settings can be toggled.
Steps
1. In the Layer palette, right click the ruler icon on the layer you want to delete the ruler from.
*For Smartphones/Tablets users, long press the icon.
2. From the menu that is displayed, select Delete Ruler.
*By toggling Show Ruler, it is possible to temporarily hide the ruler.
Here are some other ways operate the ruler.
Deleting the Ruler
From the Layer menu, select Ruler - Frame→Delete Ruler.
Drag the Ruler icon to the recycle bin/trash.
Hiding the Ruler
From the Layer menu, toggle Ruler - Frame→Show Ruler.
Click the Ruler icon while holding the shift key.