On 21/06/2019 09:31, Robin wrote:

They should be recalibrated after 20 years.

A few have extended periods - a very few up to 40 years.

But as they tend to slow down (under-read) with age I'd not rush to
complain.

Some even go backwards when solar panels are exporting to the grid just
like a battery of absolute efficiency with infinite capacity but free
and takes up no space.

So I've heard...