A double-line field book is similar to its single-line counterpart, except it has a red line in the center, as well as two blue or red lines that are about 1.5 cm apart and are ruled down the center of each page. These spaces represent the chain line and are meant to record any changes that need to be kept separate. Feel free to look the broad selection of field books that we have in stock, so you can find what works for you.