Here's how to convert 23,500,000 nanometers to millimeters:

* Know the conversion: 1 millimeter (mm) = 1,000,000 nanometers (nm)

* Set up a proportion:

(23,500,000 nm) / (x mm) = (1,000,000 nm) / (1 mm)

* Solve for x:

x mm = (23,500,000 nm * 1 mm) / 1,000,000 nm

x mm = 23.5 mm

Therefore, 23,500,000 nanometers is equal to 23.5 millimeters.