[mike golding]

Of course, I'm used to piano music and forgot about those wide organ scores. Yes, the equivalent to horizontal Alternate Page turning is Half Page display mode with Landscape orientation. As I discussed in the "Alternate Page ambiguity" thread in this forum, I see (top-to-bottom) Half Page mode as perfectly analogous to side-by-side pages with Alternate Page turns:
 
"In Half Page display mode when all of a page is showing and a page turn occurs, the top half of the next page is displayed above the bottom half of the current page. These two half pages are separated by a horizontal bar. The next page turn displays all of the next page and the separation bar disappears. This bar serves as a clear indicator when the page halves are out of sequence and another turn is needed to see the remainder of the page".
 
I don't use this, but I think Mike may have added some refinements in MobileSheets where you can somehow indicate the exact position on the page where the split should be. I think the horizontal bar is very helpful because otherwise it is easy to forget whether the page halves are in or out of sequence (whether you have already turned the page). This especially true when you need to select a (different) good location on each page to trigger the turn.
 
This is like what I was requesting (in that other thread I referenced) for horizontal Alternate Page turns: a vertical bar to indicate when the horizontal pages are out of sequence. So to complete the analogy, when you see the bar --- if you're playing the right side (or bottom half) you know you've already turned the page; and if you're are playing the left side (or top half) you need to turn again to move forward.

Thanks for the feedback feedback ,
Mike G.