Cancels are not always easy to detect, if the stub or fold they are attached to is small; however, often there will be a difference from other leaves in matters such as paper thickness, watermarks, chain-lines, etc. Whether the old leaf had a signature or not, the new one usually has one added. It occasionally occurs as an error that the old leaf is not excised, or even that the wrong leaf is removed. To obviate this, the old leaf is sometimes partly slit.
