1 nanometer = 10-9 meter 68 nanometers = 68 x 10-9 meter It may mean more to you in this form: 0.000000068 meter
Multiply 800 by 10 to the negative 9th power, so that would be 8 by 10 to the negative 7th power.
692.1 nanometers is equivalent to 0.0000006921 meters, or 6.921 x 10^-7 meters.
Multiply by 10^-9
345 nanometers = 345 x 10-9 meters.