(Available from the Dock icon, too)
Opens a horizontal ruler.
The orientation of a ruler can be changed at any time, (i.e horizontal to vertical, or vertical to horizontal) by clicking this button inside the ruler:
A ruler can be closed with this button:
The size of a ruler can be changed with the resizer:
The transparency of a ruler is set in the Settings
dialog.
Opens a vertical ruler.
Opens a ruler for both height and width of a layout.
All faded rulers will be shown again.
All visible rulers will be faded.
Closes all opened rulers.