A blood glucose measuring device and method for transmitting measured bG values to an external device such as a computer with improved data integrity for greater reliability is disclosed. The measuring device comprises a measuring means for determining measured blood glucose values, a measured value memory in which the measured blood glucose values are stored, a data interface that is configured for a data exchange with an external data reading apparatus, and a data file system which comprises a data reading application which can be accessed by the external data reading apparatus in order to read the stored measured blood glucose values, wherein the data system file further comprises a test application that is configured to execute an integrity test for the data reading application by forming a current digital signature for the data reading application and comparing this with a digital test signature provided in the data file system.