Bought this book last night
https://www.amazon.com/gp/product/1785282395/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Reading the Kindle version while the real thing comes in next week. Whatever I don't understand, I'll make sure to come here and ask the Pro's. Let's begin with UID's. Why do they need to be above 499? What is so special about UID's 499 & below?