What should be entered in the box at the upper right-hand corner of the note card?

A note card, or index card, is used for recording and storing small amounts of data gathered for a research. Typically, what should be entered in the box at the upper right-hand corner of the note card is the source of the information. That is to say, the name of the author or the page number where the information quoted in the note was found

fertile good for trade etc