[caf]

It doesn't need two meters, you can just keep separate track of the times that the connection is a net exporter and the times it is a net importer.

[mmt]

That's true, in that, if the metering is purely electronic, the only thing "separate" would be two different readouts. For electro-mechanical metering, I'd still expect a need for two physically separate ones.

Regardless, substituting "readouts" for "meters" is irrelevant to my question.