Use A Ladder On The Stairs- Ladder Stairwell Hack - GardenFork - YouTube
Werner PK80-2 Level-Master Automatic Ladder Leveler by Werner: Amazon.co.uk: DIY & Tools
The Best Ladders | Reviews by Wirecutter
Little Giant Ladders Leveler M17 with Leg Levelers Aluminum 18-ft Reach Type 1A - 300 lbs. Capacity Telescoping Multi-position in the Multi-Position Ladders department at Lowes.com