Ardour's Ruler
Ardour's Ruler

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.