I have needed a long measuring tool that is rigid for checking square on doors (measuring the diagonals). I bought this a bit reluctantly because it is in three pieces and I don’t normally trust rulers that come apart. This is dead-on accurate and the joints where it comes together are precision milled and I love this tool.

https://youtu.be/CSB6o1yc7CY?si=at_zDASgroHjLXAk