What is the ANSI standard for sphere power measurements up to 6.50D?

The ANSI standard for sphere power measurements up to 6.50D is 0.13D. This standard signifies the level of accuracy that is required when measuring spherical power in prescription lenses. A measurement tolerance of 0.13D indicates that any deviation from the prescribed power within this limit is deemed acceptable according to the standards set by the American National Standards Institute (ANSI).

This level of precision is critical for ensuring that the lenses provide optimal visual correction and comfort to the wearer. Understanding these tolerances is fundamental for opticians as they help maintain quality control in the fabrication of prescription lenses. Other options provided in the question represent different tolerance levels that are either not applicable to this specific range of sphere power measurements or do not meet the ANSI standard for accuracy in this context.