What is this multiplier showing on my workout screen?

Hello,
So I have a workout of type running prepared.
So I'm starting the run activity, selecting the workount and I get this screen:

https://photos.app.goo.gl/XNFbZPemedjhevD38

My workout is a 50 minutes run in HR Zone 2. 

So .. what is this multiplier showing? The gauge is in the midle of the green areya when the multiplier is 1.5 so I guess is some king of metric how close to the desired zone I am. 
Can I have some documentation about that? 
And can I change the layout of this screen?

Thanks!