If you have a Accu-check Performa, you will know that the strips come with a expiry date.
If the strips have expired, you will not be able to use them, even if you manually change the devices date.
This is because the device has a second battery onboard, which powers another clock, which is set in the factory.
There are several hacks online showing you how to get around this problem, some which involve shorting out this second battery. This does work, however I am not into shorting out batteries.
There are two screws on the back of the case, one is under the label. (yes, goodbye warranty)
Then lever the case open, by pushing back on the internal case tabs in these locations.
The best method is to use a soldering iron to lift one side of the battery (point 1) of the board, then use a wire to momentarily short the contacts on the board (point 1 & 2) to totally discharge the real time clock circuit.
If you are no good with a soldering iron, I suggest that you don’t do this procedure. Also you should not rely on expired strips, because they are “expired”