Understand the Review of test runs

Wanted to ask what Tyr means when looking at the review of the 5 laps during practice.

I'm guessing its Tyre wear but i dont understand the reducion of numbers from 50 to 47 in 5 laps.

If it is tyre wear why is not starting at 100.

And advice will be helpful.

tyre pressure

so it has nothing to do with wear then?

no how quick they warm up. The higher the quicker they warm and the lower the slower they warm tivaries at every track as some tarcks may be wuite high speed so you need lower as the tires war up wuicker whereas monaco for example is quite low spped so u need higher. But the driver/team decides this anyway

thanks that helps alot

The columns in the review screen correspond with the seven car setup sliders.