To measure the length of a curved line on paper, use a flexible measuring tape or a string.
How to determine the length of a curve line on paper?
In continuation, one need to align the tape or string along the curve, ensuring it follows the exact path without gaps or overlaps. For more precision, break down the curve into small, straight segments and measure each one separately, summing their lengths.
Alternatively, use a ruler to measure the straight segments of the curve and then employ mathematical approximations or software tools for curved portions. Accuracy depends on the curve's complexity, so adapt your method based on the line's characteristics, aiming for the most precise measurement possible within the constraints of the medium.