We describe the calorimeter system serving the HELIOS experiment at CERN, its calibration, and its performances measured in test experiments. The calorimeter signal for hadrons was found to be proportional to the energy to within 2% over the energy range 8-200 GeV. Over the same energy range the energy resolution σ E scales as 1 E for both electromagnetic and hadronic showers. The values found were (0.215 ± 0.007) E and (0.337 ± 0.012) E, respectively, for the detection of single particles. The signal ratios e/mip and e π are 0.70 ± 0.05 and 0.984 ± 0.006, where the latter ratio was found to be dependent on the signal integration time the quoted number being obtained for a 130 ns gate. The energy resolution for multiparticle detection was found to be about twice as large as for the detection of single particles in the actual calorimeter configuration. The energy flow logic, designed to provide trigger information on physics quantities such as transverse energy and missing energy, was shown to be very accurate and reliable.