I've had one planner in my lifetime.
when I was a department manager for Sainsburys I thought it would be smart to have one for recording sales. I needed something that would fit in the breast pocket of my polyester brown work suit (shudder), so my mum bought me the tiniest one from WH Smiths for Christmas 1989 or 1990. The pages are a minute 8cm x 12.5cm. It didn't work for me, so it has been stored away ever since.