NCR paper rolls have positive and large specifications, but there are different prices for top paper, medium paper and bottom paper. If the front of the paper touches the front or the back of the medium paper, the front of the paper can be copied. Two sheets oftoppaper or two sheets ofmediumpaper can not produce a copy effect. Because the reverse side of thetoppaper, the positive side and the negative side of the medium paper, and the positive side of the paper have chemical molecules that can be duplicated on its surface. There is no paper on the front and no paper on the back. It would cost a lot to make both sides of the paper with a copy effect. Therefore, the top and bottom paper are cheaper, but the middle paper is the most expensive of the NCR paper  rolls. This kind of paper is not obviously different from ordinary paper in appearance, but it can be used to copy and produce the same effect as blue copy paper (note: Carbon-free paper produced in Europe, America, South Africa and other countries is black), and it does not stain fingers and clothing, and is more convenient for sanitation. Because this paper is not made of carbon, it is called carbon-free paper, or carbon-free paper for short. When using documents printed on carbon-free paper rolls, they are usually separated by a small piece of cardboard, so as to avoid writing too hard and cause other copies of the underlying documents to be copied! NCR paper can be roughly divided into five colors; white/red/blue/green/yellow and other five colors play a role in distinguishing sheets! The names of NCR paper are: white (upper white/middle white/lower white), red (upper red/middle red/lower red), blue (upper blue/middle blue/lower blue), green (upper green/middle green/lower green), yellow (upper yellow/middle yellow/lower yellow).