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.
A square nanometer (often abbreviated as nm²) is a unit of area in the International System of Units (SI) and is used to describe extremely small areas, especially in the context of nanotechnology and scientific research.
One square nanometer is equal to one billionth of a square meter (1 x 10^-9 m²). In other words, it takes one billion square nanometers to make up one square meter.
To give you a sense of scale, a square nanometer is incredibly tiny. It's often used to describe the size of individual atoms, molecules, or the features on nanoscale devices. Nanotechnology deals with structures and materials on this extremely small scale, where traditional units of area, like square meters or even square millimeters, are impractical.