How do I change a value based on screen center?

So I would like to read the screen center X value. Any ideas on how to do this would be appreciated. Guessing that their are many ways to do this. Was sizing things based on their Y value but hope use this value to keep thing connected vs just getting smaller.

Crude example:

.........

'''''''''

*********

XXXXXXXXX

Vs

. . . . . .

' ' ' ' ' '

* * * * * * * * *

XXXXXXXXXXXXXXXXXX

The screen center is in the middle between ViewPortLeft(L) and ViewPortRight(L), where "L" is layer name or number.

So you can use lerp(ViewPortLeft(L), ViewPortRight(L), 0.5)