Which notation is used to express Dk/t magnitudes like 24 x 10^-9?

Which notation is used to express Dk/t magnitudes like 24 x 10^-9?

• A. × 10^-3
• B. × 10^-9
• C. × 10^-6
• D. × 10^9

Answer: (B)

Dk/t values for contact lenses are very small, so the standard way to express them is as a multiple of 10^-9. Writing something like 24 x 10^-9 keeps the number compact and directly shows the tiny magnitude, which makes it easy to compare different lens materials. If you used ×10^-3, ×10^-6, or ×10^9, the values would look either far too large, far too small, or be awkward to read, and they wouldn’t match the convention used in this field. So, the conventional notation for expressing Dk/t magnitudes around tens to a few hundreds is ×10^-9.

Dk/t values for contact lenses are very small, so the standard way to express them is as a multiple of 10^-9. Writing something like 24 x 10^-9 keeps the number compact and directly shows the tiny magnitude, which makes it easy to compare different lens materials. If you used ×10^-3, ×10^-6, or ×10^9, the values would look either far too large, far too small, or be awkward to read, and they wouldn’t match the convention used in this field. So, the conventional notation for expressing Dk/t magnitudes around tens to a few hundreds is ×10^-9.