Has anyone tried the Shape Up method by Basecamp? Their concept of “fixed time, variable scope” seems like it might break the Gordion Knot of software estimatio

Has anyone tried the Shape Up method by Basecamp? Their concept of “fixed time, variable scope” seems like it might break the Gordion Knot of software estimation challenges. Their book is available for free online, here's a link to the chapter "Estimates don’t show uncertainty " https://basecamp.com/shapeup/3.4-chapter-13#estimates-dont-show-uncertainty https://basecamp.com/shapeup/3.4-chapter-13#estimates-dont-s...