A measurement device, which communicates data to at least one system, and which has the capability of identifying measurement data returned by the system via the data communication as its own, and the capability to rule out manipulation of measurement values and to thus provide this returned measurement data reliably for further processing / evaluation or displaying, which comprises: • at least a communication interface to components of a system, which at least has the capability of receiving signed and or encrypted measurement data, storing said measurement data in a memory and delivering back, and has the capability of offering time information related to a time reference, • at least a measuring module, which assigns measurement signals to measurement values, whereas measurement values are energy measured values or counts supplied by at least one sensor, • at least a memory for the last determined measurement value, • at least a memory for a time stamp, which in the time module was determined for the last generated measurement value, • at least a time adjustment module, which checks and adjusts the time, offered by said communication interface of the system, to the local time of the time module, • at least a memory for the identification assigned to said measurement device, • at least a memory for one or more of the keys required for encrypting and/or signing, • at least an encryption and/or signature encoder that, using the key in said key memory, supplies the information offered to the aforementioned memories (IS, MS and ZS), including the validity and reliability identifier, with information for inspecting the integrity of the data, compiles said information into a current data set and transfers it to at least said communication interface for transfer, wherein only one part of the last data sets or their content is saved in the measurement device, and • at least an encryption and/or signature decoder that, using the key in said key memory, can inspect the data sets returned via the communication interface for integrity of the data content and the identification of the measurement device and upon successful inspection of this data supplying said data for further processing or evaluating or displaying. • at least a communication interface to components of a system, which at least has the capability of receiving signed and or encrypted measurement data, storing said measurement data in a memory and delivering back, and has the capability of offering time information related to a time reference, • at least a measuring module, which assigns measurement signals to measurement values, whereas measurement values are energy measured values or counts supplied by at least one sensor, • at least a memory for the last determined measurement value, • at least a memory for a time stamp, which in the time module was determined for the last generated measurement value, • at least a time adjustment module, which checks and adjusts the time, offered by said communication interface of the system, to the local time of the time module, • at least a memory for the identification assigned to said measurement device, • at least a memory for one or more of the keys required for encrypting and/or signing, • at least an encryption and/or signature encoder that, using the key in said key memory, supplies the information offered to the aforementioned memories (IS, MS and ZS), including the validity and reliability identifier, with information for inspecting the integrity of the data, compiles said information into a current data set and transfers it to at least said communication interface for transfer, wherein only one part of the last data sets or their content is saved in the measurement device, and • at least an encryption and/or signature decoder that, using the key in said key memory, can inspect the data sets returned via the communication interface for integrity of the data content and the identification of the measurement device and upon successful inspection of this data supplying said data for further processing or evaluating or displaying.