I would like to apply this formula to several cells in sheet:

=Sheet2!A1+Sheet3!A1

When I copy this formula to the next cell below it I would like it to show:
=Sheet2!A7+Sheet3!A7

next cell would be:

=Sheet2!A13+Sheet3!A13

BUT when i drag the fill handle it does not follow the step (6) I gave it to
follow?!

Thanks!