20) What is the name for classification of letters having the elementry strokes of even width?

21) What is the name for part of circle with radii making 90? with each other?

22) What is the name for part of circle, between any two points on the circumference or periphery?

23) Which is the survey, if the surface of the earth is assumed as plane?

24) Which agency in India conducts Geodetic survey?