NCR - No Carbon Required - sets have a wide range of uses; Invoices, Purchase Orders, Delivery Notes, Time / Work Sheets.......

They can be printed as either 2 part or up to 8 part or any amount in between. Papers come in a variety of colours.
Top sheets can be thicker - recommended for multi coloured printing and bottom sheet is available in card if required, perhaps for a work ticket etc.
Once printed, they can be numbered at an extra charge of 15%.

Finally the sets can either be glued into loose sets, which is included in the prices shown, or made into books at 50 pence each with one or more parts perforated.

When using books of NCR sets, whilst it is not necessary to use carbon, a sheet of card is needed to separate the top set from the ones below, to prevent the impression of the pen marking the sets underneath.