Typically you would use OnSong to send tempo changes to MIDI-connected devices. This allows OnSong to control your MIDI setup and maintain the proper song information in its library. However, there are times were you may want to listen for the tempo of another in your MIDI signal path.
For instance, you may have a guitar effects processor that implements a tap for tempo button for setting the timing of delays. You may want to record that BPM into the song you are currently viewing. To acquire the tempo, open the Tempo Picker either by tapping and holding on the Metronome Button in the Live Bar, or by tapping on the "A"/cursor icon in the Menubar to open the Song Editor and then tap on the information icon to open the Metadata Menu and choose Tempo.
Once open, locate the Acquire from MIDI Clock switch and turn it on. OnSong will then listen for MIDI clock information and set the tempo. Since the tempo is calculated from the incoming clock, keep this switch enabled until the BPM stabilizes. Once received, turn off this switch, or close the menu to stop listening to MIDI clock events.
It's important to note that MIDI clock requires a hard-wired connection. Sending MIDI clock over Bluetooth or WiFi will cause shifts in the tempo due to latency.