Extrusion and first layer test part

I designed this part to help me tune :
- The extrusion (flow) in my slicer (I use Cura)
- The z offset for a good first layer

What you want to look for here is especially the top edge of the part, if the plastic on the inside of the wall is squished up then you are probably over extruding like I was. I have attached a picture showing this.

What I ended up finding was that I had to turn down flow to 75%.