[GraemeJ]

Not necessarily of use to MS users, but I find many apps - presumably originally designed with a 'phone in mind - will default to a portrait mode.  This has two implications;

1/ If you have your device on a music stand, you will have the connectors on the upper edge - most 'phones would be used with the connectors on the lower edge. If there is no auto-rotate, often the case, then your view will be upside down. 

2/  Using a large tablet, then you might find it more convenient to hold that in landscape mode, then the view is rotated 90º

There are a number of apps available which will force the mode you want, no matter what the designer intended.  I like Ultimate Rotation Control, which allows the forcing of individual apps to a specific display mode, but there are plenty to coose from.