WYFFOS has scattered light like whichever spectrograph. It is important to subtract the scattered light, principally in the case of faint objects. We recommend apscatter (load noao, imred and specred packages) to do this operation (see Appendix I). Firstly, if the definition and the tracing of the apertures was not done, this task allow us to do it. Secondly, a polynomial fit is done along the spatial direction: a polynomial fit is used to reproduce the enveloped of the intensity values from the spaces between fibres. Finally, a polynomial fit is done along the dispersion axis.