Tachograph for a motor vehicle , wherein a control circuit is provided in the tachograph , which control circuit is configured to repeatedly acquire a respective current value for a multiplicity of measured variables during a journey of the motor vehicle and to transmit messages of at least one message type via a communication connection , wherein the respective message type specifies at least one transmission time for the transmission of the respective message of this message type and a selection of the measured variables the respective current value of which should be contained in the message and a format in which the respective current value should be indicated in the message , and wherein the control circuit is configured to generate the respective message of the respective message type for the at least one transmission time , wherein the respectively generated message , in relation to the respective selection of the measured variables, contains their respective current value in the respective format, wherein, in the control circuit , message types are able to be configured at runtime of the tachograph and the control circuit is to this end configured to receive configuration data for at least one user-defined message type via a configuration interface , wherein the control circuit is configured to compile and transmit the messages of the user-defined message type in accordance with the configuration data at the at least one transmission time specified by the user-defined message type and, during the compilation, to ascertain the respective current value of each measured variable selected by the user-defined message type and to convert same into the specified format, wherein the control circuit is configured to keep ready a message-independent value reservoir of the current values in a data memory and to query the at least one value that is required for the message from the value reservoir in order to generate a user-defined message from the value reservoir on the basis of the configuration data , and to operate a conversion module in order to convert the respective current value into the format required for the respective message , which conversion module is configured to carry out at least one predetermined formatting step on the basis of the configuration data . in the control circuit , message types are able to be configured at runtime of the tachograph and the control circuit is to this end configured to receive configuration data for at least one user-defined message type via a configuration interface , wherein the control circuit is configured to compile and transmit the messages of the user-defined message type in accordance with the configuration data at the at least one transmission time specified by the user-defined message type and, during the compilation, to ascertain the respective current value of each measured variable selected by the user-defined message type and to convert same into the specified format, wherein the control circuit is configured to keep ready a message-independent value reservoir of the current values in a data memory and to query the at least one value that is required for the message from the value reservoir in order to generate a user-defined message from the value reservoir on the basis of the configuration data , and to operate a conversion module in order to convert the respective current value into the format required for the respective message , which conversion module is configured to carry out at least one predetermined formatting step on the basis of the configuration data . <EOS>