property Pages.PosToIndex (Position as Long) as Long
Gets the page's index giving the page's position.

TypeDescription
Position as Long A long expression that indicates the position being translated
Long A long expression that indicates the converted index 

Use the PosToIndex property to convert positions to indexes. 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 IndexToPos property to convert indexes to positions.