EN is the abbreviation for Europese Norm (European Norm). In NEN, the extra N stands for Nederlandse norm (Dutch norm), so the desk chairs that meet this norm are suitable for Dutch people. Generally, a NEN 1335 desk chair is suitable for people with a body length between 151cm and 192cm. The difference in body length between Europeans is large, so the margin in length is high as well. A desk chair with this norm is good for an ergonomic posture. You work for hours at a day at the office or at home at your desk, so it's important to at least have good posture.