Using Marks


	Under Sea Adventurers Dive Club

How To Use Marks Or Ranges

Ray McAllister

Marks or ranges can be used to find a point at sea with very great accuracy if you follow the rules and suggestions below.

Rule 1. Only one straight line in all the world can go through two different points. Put differently, it says that if you line up two chosen points so that they touch or merge, you are on a specific line. This line is also called a "range".

Rule 2. Two straight lines can cross at only one point. Thus, if you line up a second set of points, the new straight line, cutting the one in Rule 1, determines your exact location.

Other helpful rules based upon geometrical considerations, etc. are:

Rule 3. For maximum accuracy, be sure points chosen are sharp and clear, for example, the peak of a roof, the side of a building, a radio antenna, tree trunk, or water tower leg.

Rule 4. Wherever possible, chose two points which are widely separated. The farther apart they are, the better defined is the straight line they determine. Generally, the best combination is an object near or west of the Intracoastal Waterway over one near the beach.

Rule 5. Maintain an angle of 60 to 120 degrees between the two lines or ranges for greatest accuracy.

Rule 6. Be meticulous about your marks. If you are exactly on your marks, you are exactly over your fishing and diving spot. To use the marks in the illustration, note the two points indicated on the North Mark. Line up these two points exactly. Now, keeping the marks exactly as shown in the photograph, run seaward or landward until the other set of marks looks exactly like the Middle or South Mark photo. At that point, drop a small buoy, circle and anchor as desired