It is technologically possible to measure the frequency of laser light to extraordinarily high accuracy by counting the oscillations of the light wave with the help of a frequency comb. This allows time to be measured by counting the number of oscillations of the laser light, which has been stabilized to a particular atomic transition. Such a device is known as an optical atomic clock. One prominent example for an optical atomic clock is the ytterbium (Yb) lattice clock, where a particular electron transition in the ytterbium-171 isotope is used for laser stabilization. In this case, one second has elapsed after 518 295 836 590 863.63 ± 0.1 oscillations of the laser light stabilized to the corresponding electron transition. Other examples for optical atomic clocks of the highest accuracy are the ytterbium(Yb)-171 single-ion clock, the strontium(Sr)-87 optical lattice clock and the aluminum(Al)-27 single-ion clock. The achieved accuracies of these clocks vary around 10, corresponding to about 1 second of inaccuracy in 30 billion years, significantly longer than the age of the universe.