Measuring Range

The range of lengths that can be measured is very large. Atomic nuclei have diameters in the range of l = 10^-15 m. The diameter of our Milky Way is in the range of 10²¹ m. No measurement system can cover the entire measuring range of length measurement at once. Instead, there are very different measurement methods for the individual ranges. A measuring instrument generally specifies a measuring range as the range of the measured quantity within which it meets its specification with regard to the maximum measurement deviation. Outside the measuring range, it may still be possible to measure, but possibly with lower accuracy.
The best length measurements today achieve relative measurement uncertainties of about 10^-11 to 10^-12. For a bar 1 m long, this would mathematically give about 1 pm; in practice, temperature fluctuations, for example, limit the achievable uncertainty to a few nanometres. For the distance between the Earth and the Moon (384400 km), laser ranging achieves a measurement uncertainty in the millimetre range. So the measurement uncertainty depends on the measuring range of the measurement system.