You can either delete the last measured value or all the data of the concerned user profile.
For the deletion of the last measured value please press the M-Button to arrive at the storage retrievement mode with all your measured data. After that press and hold the S-Button for 7 seconds. The last measured value flashes a few times then the word "del" will appear on the display. With that your last measurement value is deleted.
If you want to clear the whole user profile from its stored measurement data you also need to press the M-Button to reach to the storage retrievement mode but then press and hold the M- and the S-Button at the same time for approx. 10 seconds. This time "del ALL" appears on the display. Confirm with the S-Button. With "del OK" you are informed about the complete deletion of all the measurement data on this particular user profile.