Chapter 3 aircraft?

Can someone please shed some light on this for me…

What is meant by the different ‘chapter’ classification of aircraft in the UK?

I know that the most common classification is Chapter 3, but even this category is split down into High, Base and Minus sub-categories.

I am very confused… :confused: …but am interested to know which ‘chapter’ a Boeing 737-800 and 757-200 would be classified into…?

Any ideas, please feel free to explain.

Many thanks.

Jonathan Davies.