I assumed the post title meant nanometers. Why? Floating-point rounding bugs. A nanometer is about 9e-15 degrees of latitude, which is right about where a double-precision floating point number runs out of digits. So, if a piece of software uses exact `==` equality, it could easily have a bug where two positions 3600 nanometers apart are seen as being different, even though they should be treated as the same.