A square decameter (often abbreviated as dam²) is a unit of area in the International System of Units (SI). It represents a square with sides that each measure 10 meters (1,000 centimeters) in length.
One square decameter is equal to 100 square meters (m²) because each side of the square is 10 meters long, and when you square that length, you get 100 square meters.
Square decameters are not as commonly used as some other units of area, but they can be used to describe moderate-sized land areas, and they are a part of the metric system for measuring area.
The "acre (US survey)" is a unit of area used specifically in the United States for land surveying and legal property descriptions. It is different from the standard acre used in other parts of the world. The U.S. survey acre is based on the U.S. survey foot, which is a historical unit of length used in land surveying in the United States. The U.S. survey foot is slightly different from the international foot.
One acre (US survey) is equal to approximately 4,046.872609874252 square meters (m²) or about 0.40468726 hectares (ha).
This unit is used in various land-related applications, especially in the United States, where the U.S. survey acre is employed for legal and historical reasons in land surveys, property descriptions, and land records. It's important to be aware of the specific units being used when dealing with land measurements in the United States to avoid discrepancies or errors.