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Scope is the nautical term used to describe the water depth, to length of rode ratio to get anchors to hold well in different wind/current conditions.To get the TRUE scope height from the bottom we must add the height of the anchor point above the water to the water depth.
Example:If we have an anchor point height 5' above the water and a depth of 20' ,we have a true scope height of 25'.We then multiply the by the correct scope for the conditions.
ie: 6:1 for calm conditions.
8:1 for moderate conditions.
10:1 for rough/windy conditions.
So 25'x 6 = 150'of rode for calm.
25'x 8 = 200' of rode for moderate.
25'x 10=250' of rode for rough/windy conditions.
With all chain rode you can 1/2 these figures to obtain the same holding power.