I am reading some technical documents and there is a list of items that make up the product. Throughout the document where there are multiple items, they are listed as 2 off, 3 off and so on.
For example it would be similar to this:
My product comprising of:
- 2 off card 1
- 1 off card 2
- 1 off transit case
Is this correct? I thought it should be 2 of, 3 of and so on. I would like to know if the usage is correct and if possible why off is used in this context.