The procedure will be described that is developed for assigning wavelengths to the UV stellar spectra obtained in 1976 by means of a balloon-borne instrument consisting of telescope with starpointing system, echelle spectrograph and SEC vidicon. The instrument covers the spectral region of 2000 Å to 3400 Å with a wavelength resolution of 0.1Å. The wavelength assignment aims at an accuracy of 0.01 Å. Results will be presented and difficulties encountered, related with the use of echelle spectrograph and SEC vidicon detector, will be analysed.