The O-group Numerals Glossary Italic is an historical style, and has inherited several features from chancery cursive. The descender of the letter f turns to the left, for example.
Chancery cursive is a fifteenth-century style, and needed some adjustments.
It was usually written with a broad-edge pen, which makes beautiful thick and thin lettershapes. Nowadays, most people write with pencils and ballpoints and fibretips. That's why the model is monoline, without thicks and thins. In our version, the ascenders and descenders are shorter. The letter c is more rounded than it used to be.