Bars:Beats
BBT markers allow resetting the timeline to a particular bar and beat. Most of the time a BBT marker will reset it to 1|1|0 (the very first beat of the very first bar) so that for each song in a multi-song session there would be a musical time origin. However it's entirely possible to reset to an arbitrary value such as 7|3|0.
To create a new BBT marker, -click on the Bars:Beats ruler. This will open a dialog titled New Music Time where you can name the marker and define what bar (left field) and beat (right field) this marker should reset the time to.
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The timeline grid and the ruler will be updated accordingly:
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Dragging a BBT marker right or left will reset the musical time at a different position on the timeline.
Right-clicking on a BBT marker opens a menu with two options: Edit… and Remove.
Choosing Edit… opens the Edit Musical Time dialog where it's possible to rename the marker and set a different bar and/or beat to reset the musical time to:
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Choosing Remove deletes the marker.