property Pages.IndexToPos (Index as Long) as Long
Gets the page's position giving the page's index.

TypeDescription
Index as Long A long expression that indicates the index being converted.
Long A long expression that indicates the position of converted index. 

Use the IndexToPos property to convert indexes to positions. Some of the control properties like Active, returns position instead page's index, so the position needs to be converted to a index, if the Item property is used.  Use the PosToIndex property to convert positions to indexes.