Final answer:
On a lens clock, convex curves are read as positive. This positive measurement indicates a convex or converging lens, which focuses parallel light rays into a single point.
Step-by-step explanation:
On a lens clock, convex curves are read as positive measurements. This is because the lens clock is designed to measure the curvature of lenses in diopters, and a positive reading on a lens clock usually indicates a convex or converging lens. These types of lenses converge light rays that enter the lens parallel to its central axis into a single focal point on the opposite side. Convex lenses are thickest at their center and are commonly used in eyeglasses for farsighted people, magnifying glasses, and other optical instruments where magnification or the correction of farsightedness is desired.