Where is the Relative Zero button?

I have read about the Set Relative Zero button in the documentation https://wiki.librecad.org/index.php/Relative_Zero but I cannot find that button anywhere.

Can anyone point it out to me?

They are part of the "Snap Selection" toolbar.

To enable this toolbar: Menu: Widgets > Toolbars > "Snap Selection"

Many tools also sets relative zero to the latest point selected by user