A laser tracker (40, 90) for continuously tracking a reflecting target (42, 97) and for determining a distance to the target (42, 97), comprising • a base defining a vertical axis, • a beam guiding unit for emitting measurement radiation (11, 41, 96) and for receiving at least part of the measurement radiation (11, 41, 96) reflected at the target (42, 97), wherein the beam guiding unit can be pivoted in a motor-driven manner relative to the base about the vertical axis and an inclination axis which is substantially orthogonal to the vertical axis, • an interferometer for determining a change in the distance to the target (42, 97) using interferometry having a tunable laser diode configured as the interferometer laser beam source for generating the measurement radiation (11, 41, 96) for the interferometer in such a way that the measurement radiation (11, 41, 96) is coherent and longitudinally single-mode, • an absolute distance measurement unit for determining a measurement distance value for a distance (45, 46) to the target (42, 97), and • angular measurement functionality for determining an orientation of the beam guiding unit relative to the base, characterized by a control and evaluation unit configured such that, during execution of a calibration mode, an interferometer wavelength of the measurement radiation (11, 41, 96) is determined by • carrying out defined sample measurements while varying the distance (45, 46) to the target (42, 97), wherein ∘ the sample measurements take place for at least two different distances (45, 46) to the target (42, 97), ∘ the measurement radiation (11, 41, 96) is continuously aligned with respect to the target (42, 97) and an interferometer output variable is determined with the interferometer for each of the at least two different distances (45, 46) to the target (42, 97) while keeping the interferometer wavelength stable, and ∘ at least two measurement distance values for the at least two different distances (45, 46) to the target (42, 97) are provided in each case by determining a distance using the absolute distance measurement unit, and • determining the interferometer wavelength of the measurement radiation (11, 41, 96) at least on the basis of the at least two measurement distance values and the respectively determined interferometer output variables. • a base defining a vertical axis, • a beam guiding unit for emitting measurement radiation (11, 41, 96) and for receiving at least part of the measurement radiation (11, 41, 96) reflected at the target (42, 97), wherein the beam guiding unit can be pivoted in a motor-driven manner relative to the base about the vertical axis and an inclination axis which is substantially orthogonal to the vertical axis, • an interferometer for determining a change in the distance to the target (42, 97) using interferometry having a tunable laser diode configured as the interferometer laser beam source for generating the measurement radiation (11, 41, 96) for the interferometer in such a way that the measurement radiation (11, 41, 96) is coherent and longitudinally single-mode, • an absolute distance measurement unit for determining a measurement distance value for a distance (45, 46) to the target (42, 97), and • angular measurement functionality for determining an orientation of the beam guiding unit relative to the base, • carrying out defined sample measurements while varying the distance (45, 46) to the target (42, 97), wherein ∘ the sample measurements take place for at least two different distances (45, 46) to the target (42, 97), ∘ the measurement radiation (11, 41, 96) is continuously aligned with respect to the target (42, 97) and an interferometer output variable is determined with the interferometer for each of the at least two different distances (45, 46) to the target (42, 97) while keeping the interferometer wavelength stable, and ∘ at least two measurement distance values for the at least two different distances (45, 46) to the target (42, 97) are provided in each case by determining a distance using the absolute distance measurement unit, and ∘ the sample measurements take place for at least two different distances (45, 46) to the target (42, 97), ∘ the measurement radiation (11, 41, 96) is continuously aligned with respect to the target (42, 97) and an interferometer output variable is determined with the interferometer for each of the at least two different distances (45, 46) to the target (42, 97) while keeping the interferometer wavelength stable, and ∘ at least two measurement distance values for the at least two different distances (45, 46) to the target (42, 97) are provided in each case by determining a distance using the absolute distance measurement unit, and • determining the interferometer wavelength of the measurement radiation (11, 41, 96) at least on the basis of the at least two measurement distance values and the respectively determined interferometer output variables.