This is a term that you will come across regularly when you shop for this tool. It is also one that has not been talked about a whole lot, thus far, so let’s talk about what it is. To keep it short and sweet, the lubber line is a fixed line (it is often red) and it is used to dictate which direction you are going to be traveling. Basically, you set this lubber line beforehand (with your arm straight out) and then you can view it without doing so again.