Ah, a machinist with a question... Then perhaps an Engineer can help with an answer.

First, a disclaimer---I assume because you are using Barb's book that you intend to make a Traditional Style Kilt. You're not going to try to adapt or change anything. If you are,(other than using a VERY light weight fabric)you will just confuse yourself. Barb is the expert here. Follow the book. Follow her instructions and answers she posts here.
I am not a Traditional Style Kiltmaker. Anything I say here does not count if it disagrees with Barb in any way.
But, I probably understand the way your brain works. I understand numbers and measuring.

So, give us the numbers you have so far. We need:
Your Hip measurement,
Waist measurement,
Your Drop,
Your split numbers,
The total amount of fabric you have to work with.
What Tartan your fabric is,
And it can be helpful to know your height and weight.

When you post these we can start.