Online Guide
Brannock Measurements
Foot Tracing
Circumferential Measurements
Modified Last
I bought a good measuring tape took a bunch of measurements and double-checked them.
Prof Barnets asked for some specific ones and gave some images to show exactly what they wanted, which helped a lot. Particularly, they wanted a tracing of both feet, the length, ball circumference, high instep circumference, calf circumference at the tallest point of the boot (11 inches for these boots), and ankle circumference.
I gave them all these required measurements. However, I decided that I would take the time to give as many measurements as possible. I even took images of my feet at different angles while standing. I also gave them my Brannock size with images of my feet in the device. The guide that I found extremely helpful in this process was the custom foot measuring guide and measurement sheet on Baker's Boots website. I highly recommend this to anyone getting a MTM boot or shoe. They even have a helpful video. Here is the link to the page with everything (https://bakershoe.com/pages/foot-measuring).
Using these measurements, Prof Barnets determined the appropriate last for my foot and then modified it by adding material where needed to get a perfect fit.