[almostdigital]

This standard isn't part of the metric system though

[anonymous_sorry]

No, but the post mentions that A0 was chosen to have an area of one square metre. (Actually 0.999 square metres - you need a bit of fudge factor if you want sides in integer millimeters and a ratio of root 2)

[mkl]

I'd say it's part of it in the sense that it's based completely on it. It's not a unit or set of units though.