A dataset of 13 case studies of multi-layer cloud heights retrieved simultaneously by two ceilometers (Vaisala CL31 and Jenoptik CHM15K) has been created from measurements performed during the period from September to December 2008 at the Mace Head Research Station, in Ireland. The two instruments have been measuring close to each others providing vertical profiles of backscattered laser signal. Adopting an automated algorithm to extract the cloud base height from the attenuated atmospheric backscatter coefficient profiles it has been possible to compare the results from the two ceilometers and to assess the existing differences. Different cases have been selected with cloud layers up to a number of three with constant to highly variable cloud base. The results show the correlation coefficients ranging from R2=0.95 for multiple cloud layers with varying cloud bases to R2=0.99 for a single layer of clouds with stable cloud base. Data from the two ceilometers have been compared in conditions of no precipitation over a maximum time period of 24 consecutive hours.