The spectroscopy method compares the energy levels of spherically symmetric 2s orbitals to asymmetric 2p orbitals of hydrogen, a difference known as the Lamb shift. The exact values of the energy levels are sensitive to the distribution of charge in the nucleus since the 2s levels overlap more with the nucleus. Measurements of hydrogen's energy levels are now so precise that the accuracy of the proton radius is the limiting factor when comparing experimental results to theoretical calculations. This method produces a proton radius of about 0.8768(69) fm, with approximately 1% relative uncertainty.