The marlin ruler is the original Release Ruler. With over 2 years of research and data gathering, the marlin ruler provides an excellent reference for estimated weight. With the help of the scientific community, the sample size consisted of over 5400 marlin measurements. We know not every marlin will hit the mark but rest assured most of them will! The Marlin Ruler is double sided with contrasting easy to read colors against the bluewater where marlin are found. Keep the marlin ruler handy in a convenient area on your boat and when the times comes to reel in your next marlin, put your Release Ruler to work when you have the fish boat side. Stop guessing and know your average size and compare it to your next release! Good Luck.