It is made up of steel material with plastic holder. It is used to measure the length. One way to determine the fractional area subtended. The fractional area can then be converted to steradian.

It has two-dimensional angle space that an object subtends at a point. It is a measure of how large that object appears to an observer looking from that point. It is used to obtain the solid angle in square degrees.

A small object nearby may subtend the same solid angle as a larger object farther away for example, the small/near Moon can totally eclipse the large/remote Sun because, as observed from a point on the Earth.