https://www.ebay.com/itm/276403515343 <br /> archived copy

In 1984, Memindex was selling monthly planning calendars (pocket notebook size with spiral binding and a case) rather than their older small index card sized formats. Their calendar format looks eerily like what Day-Timer, a division of ACCO Brands, has been selling since at least the early 1990s.

This goes down to even the "cut here" triangles in the lower right corners of pages to help bookmark the current page.