Ra is the surface roughness after derusting. In the old standard, it was called smoothness, but now the new standard is defined as roughness, and the expression is different. Smoothness is expressed by code, and roughness is expressed by numerical value Ra, which is more scientific.
Smoothness and surface roughness are the same thing. Geometric error can be divided into three categories: macro geometric error (shape tolerance), surface waviness (waviness) and micro geometric error (surface roughness). At present, it is usually divided by wave distance. The wave distance less than 1mm belongs to surface roughness, and the wave distance between 1 and 10mm belongs to surface roughness, which is greater than.
Daily math learning skills
Mathematics, the first discipline that attaches importance to accumulation and understanding, is particularly important in classroom efficiency. Especially for some students whose basic knowledge is not solid enough, they should not only take notes in class, but also follow the teacher's rhythm and try to mark all the knowledge points that need to be memorized in class, and at the same time be able to classify all the knowledge points that they have not mastered and understood.
It is an important way to find out the knowledge points learned and not learned in class, so as to facilitate targeted review after class.