A power cross is:

A power cross is fundamentally a graphical representation of the power of a lens, specifically illustrating the lens' refractive power in its two principal meridians, typically the horizontal and vertical orientations. This diagram demonstrates how the lens behaves differently at various angles, providing essential information for aligning and fitting lenses accurately to a patient's visual needs.

The power cross format is crucial in understanding and calculating the effective power of a prescription lens. It represents the lens' astigmatic power, allowing practitioners to visualize how the powers in different meridians interact. By using the power cross, opticians can ensure that the fitted lenses match the optical requirements of the wearer.

The other options do not accurately encapsulate the definition of a power cross. For instance, the idea of finding a 1.53 index referenced tool curve does not relate to the primary function of a power cross, which is focused on the meridians of a lens. Similarly, while a line map of convergence can be a visual tool in optics, it is not synonymous with the concept of a power cross that directly deals with lens power. Lastly, referencing the sum of the distance power and the near add pertains more to multifocal lenses and their contributions to total power, rather than directly describing the function