The ruler scales the session along time, allows navigating, and can be marked for different uses.
One of its main uses is to move the playhead: clicking anywhere on the timeline will bring the playhead at this location in time. Also, using the mouse's scrollwheel while hovering the ruler will zoom in or out (⇑/⇓ ).
The ruler is made of a succession of rows, each having a special role related to time. Adding or removing rows can be done by right clicking anywhere in the ruler's header on the left, and ticking any of:
|Mins:Secs||scaling the session with the Mins:Secs:mSec notation|
|Timecode||scaling the session with the Hours:Mins:Secs:Frames notation|
|Samples||scaling the session with the sample number notation|
|Bars:Beats||slicing the time according to the time signature|
|Time Signature||shows the time signature. It can be changed along the timeline, by Right-click > New Time Signature. The Bars:Beats ruler will reflect the change.|
|Tempo||shows the BPM. It can be changed along the timeline, by Right-click > New Tempo. The Bars:Beats ruler will reflect the change.|
|Range Markers||allow to create and modify ranges directly on the Ruler.|
|Loop/Punch Ranges||are special kind of ranges designed to be played as a loop and to do punch recording, i.e. recording on a precise section of time, respectively.|
|CD Markers||are markers designed to be used while creating a recording that has to be split in time, as an audio CD|
|Location Markers||is meant to receive any kind of marker, user generated or from Ardour itself.|
|Cue Markers||allows triggering entire cues from the grid in the Cuewindow|
|Arrangement||allows creating range sections like a verse, a chorus, a bridge etc.|
|Video Timeline||shows thumbnails of the video in the timeline|
Most rulers allow placing markers to serve a specific purpose: mark a point in time, define a loop range, or something else entirely.
Most of the operations on the markers are described in Working with Markers, additional information on Time Signature, Tempo, Bars:Beats, and Timecode is available in the Tempo and Time Signature chapter.