What number would you read on the power wheel of a manual lensometer when the cylinder target lines are in focus for the given Rx?

When using a manual lensometer to measure the power of a lens, the focus of the cylinder target lines indicates the cylinder power of the lens. In this scenario, if the cylinder target lines are in focus at -1.50, it signifies that the cylinder in the prescription being examined has a power of -1.50 diopters.

The alignment of the lines suggests that this is the point of clarity for the cylindrical component of the lens. It's essential to ensure that the power wheel is set correctly to achieve the precise measurement corresponding to the cylindrical correction.

In the field of optics, especially in ophthalmic practice, exact values matter significantly in visual correction. Therefore, identifying the cylinder power correctly is crucial for providing the appropriate prescription to the patient. Reading -1.50 clearly indicates that the cylinder component as per the Rx is accurately measured at this value, ensuring that the lens fabricated will offer the intended corrective properties.