Mesh size variation

Dear Karl,

Thank you for your reply. I have tried using your first suggestion with tetmesh.

I want to ask about the meaning of “size”. For example, you wrote size 0.1. What is the dimension of this number? Because I would like to define the smallest mesh size to be (for example) 1km on surface 5 and the largest is 100km on surface 3.
I have a geometry more or less as shown in this problem Webcut volume with non planar surface.

Thank you for your assistance.
Alvina KK