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?

In the context of a manual lensometer, when you read the power wheel and find that the cylinder target lines are in focus, you are determining the correct cylindrical power needed to achieve a proper optical correction for an individual based on their prescription (Rx).

For a given prescription, the cylindrical power indicates the amount of astigmatism that needs to be corrected. In this case, if the cylinder target lines come into focus at -1.50, it means that this is the specific amount of cylindrical correction that corresponds to the patient's needs as outlined in the Rx.

Thus, when adjusting the power wheel to achieve the point at which the lines are sharp and clear, -1.50 is the reading that reflects the necessary cylinder power for optimal visual clarity. This outcome directly correlates with the indication of astigmatism in the prescription, confirming that the answer of -1.50 is correct as it represents accurate lens measurements for astigmatic correction.