A holding device for a breathing tube for use in lung function diagnostics is disclosed. This holding device consists of a material that is transparent for light having a wavelength in a first wavelength range but nontransparent for light having a wavelength in a second wavelength range. In other aspects, a lung function diagnostics device comprising such a holding device and a method for reading out a coding on a surface of a breathing tube for use in lung function diagnostics are disclosed.
