Staircase construction

I am finding this staircase construction fascinating (although admittedly hard to visualise).  Adrian has made up the whole design, and cut up all the pieces of wood.  I'm very trusting, aren't I?  He tells me it's all sound Physics!  Thanks to our friend Tim who came to assist with the first stages of putting it all together at the weekend.

Now we await delivery of all the oak steps and risers next week, pre-cut and appropriately aged/dried.  I can see why staircases are so expensive to buy!  In the meantime, it's back to the ladder for all trips to the bathroom ...