Why the R number is important to fight Covid-19
Governments around the world keep talking about R0, also known as the "reproduction number" or "R number".
It's a measurement that lots of countries are using when it comes to making decisions about lifting and bringing in lockdowns, what restrictions should be kept in place, and which ones should be lifted.
There's an R number for the UK and individual nations, but also for particular areas.
But what exactly is the R number and why does it matter?
BBC health correspondent Laura Foster explains what governments are aiming for and why.
Video by Terry Saunders, Laura Foster and Tobias Chapple