What is the primary unit of measurement for a single dimensional object?

In the context of measuring a single dimensional object, the primary unit of measurement is length. Length is a linear measurement that quantifies the extent of an object in one direction. For example, when measuring a rod or a line, we describe its size using units such as meters, centimeters, or inches, which are all measurements of length.

The other options represent different dimensions: weight measures the force exerted by gravity on an object, area measures the size of a surface in two dimensions, and volume refers to the space an object occupies in three dimensions. Since the question specifically refers to a single dimension, length is the most appropriate and relevant measure.