The vertical size of the paper less the top and bottom margins
is used to calculate the page count. When the print orientation
is landscape, the vertical size of the paper is the shorter dimension.
If the DataWindow object is not set to print preview, then the size of
the control determines the page number.

When Page() is in the header, it uses the first row currently
visible on the page to determine the page number. When it is in
the footer, it uses the last row currently visible. Therefore, it
is possible for the the values to be different.

This expression returns the number of the current
page:

In the DataWindow object’s footer band, this expression
for a computed field displays a string showing the current page
number and the total number of pages in the report. The result has
the format Page n of total: