The CALEC® ST MASS is a heatmeter-calculator for building-automation and energy-management. The calculator has energy- and mass-counters, some instantaneous values and two programmable auxiliary inputs including the corresponding counters or optional two relay-outputs. Data-logging is done by 28 data loggers, two billing dates and a remote controlled freeze-memory. This freeze function enables a simultaneous meter reading in a network. The meter readings, instantaneous values and some logger data are bound to LonMark® profiles using Standard Network Variable Types (SNVT). The relay-outputs can be used as actuators. The device does not need any plug-ins. The inputs for the temperature sensors are designed for the Pt 100 or Pt 500 type. They may be connected using a two- or four-wire technology. The LonWorks® networking node is realised with the Free-Topology Transceiver FTT-10A. The CALEC® ST MASS is designed as a modular device: The calculating unit module can be replaced and verified separately. The CALEC® ST MASS has all service-functions; e.g., a comfortable wink-function which also can be recognized while the cover is closed.