What is NCR
Carbonless copy paper
Also known as NCR paper, is a coated paper used to transfer information written on the front and onto sheets beneath.
No Carbon Required
(Taken from the initials of its creator, National Cash Register). It was invented by chemists Lowell Schleicher and Barry Green  as an alternative to carbon paper, (a blue sheet of carbon copy sheet is sometimes used in banking of the paying in books)though it is sometimes confused with it.
Provides an alternative to carbon copying. Tiny droplets of dye or ink are on the back of the top sheet of carbonless copy paper, and a clay coating is on the front of the bottom sheet. The dye capsules burst and react with the clay, imitating the markings on the top sheet.
When subjected to pressure or impact, the micro-capsules break and release their dye (such as from a typewriter or dot-matrix printer). Because the capsules are so small, the final print is extremely precise.
There was also a type of carbonless copy paper that was self-contained, with the ink and clay on the same side of the paper. Previously, the only options were to write documents multiple times or to use carbon paper sandwiched between the original and the copy.
Business stationery, such as invoices and receipts, that required one or more copies of the original, were printed on carbonless paper. The copies or replicas were frequently made of different coloured papers (for example, a white original for the customer, a yellow copy for the supplier’s records, and others for extra copies).
Stationery with carbonless copy paper can be provided in pads or books bound into sets, as loose sets, or as continuous stationery for printers designed to use it.