The invention relates to an optical emission spectrometer (1) being easily adjustable, and to a method (100) to set-up and operate such a spectrometer (1) comprising a plasma stand (2) to establish a light emitting plasma from sample material, and an optical system (3) to measure the spectrum of the light (L) emitted by the plasma being characteristic to the sample material, where the optical system (3) comprises at least one light entrance aperture (31), at least one diffraction grating (32) to split up the light (L) coming from the plasma (A) and one or more detectors (33) to measure the spectrum of the light (L), wherein the plasma stand (2) and the optical system (3) are directly and fixedly mounted on respective a plasma stand flange (2B) and an optical system flange (3B) which are directly and fixedly connected to each other and wherein the optical emission spectrometer (1) further comprises an analyzing unit (34) adapted to analyze the measured spectrum and to compensate for a drift of the spectrum relative to the detector (33) potentially caused by heat transferred from the plasma stand (2) to the optical system (3) considering the thermal expansion of the optical system (3).