Just as a by the way...and you probably already know this, but in the drop down menu (top right hand corner little arrow) it gives you the option to list the songbook numbers, and not the key on the songbook listing...not that this is needed for the following procedure, but I thought I would mention it.
If you double press the Songbook physical button on the panel, it opens a numerical entry box, and you can manually select the songbook entry number "on the fly" as it were...
This is the main reason I annotate the songbook listing number on the UnrealBook PDF chart....if at any time I cannot get a connection from the iPad to the PA (I have accidentally let the battery run down before a gig so need to recharge and use at the same time, or I forget a cable, or whatever), by double pressing the songbook button, and then entering manually the SB listing number as shown on the PDF, I can almost as quickly select a song on the PA...
Just another way of doing it is all
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Dennis