Accu-Chek Compact Plus Manuel De L'utilisateur page 34

The meter is unable to calculate the 90-day use-by period if
you insert a partly used drum in the meter, even if it is the same one
you have just removed,
the year, date and time settings are lost when you replace the
batteries (see Chapter 9), and a partly used drum remains in the
meter.
The meter has no way of telling you in these cases when the drum was
first inserted or how long the partly used drum has already been in the
meter.
If the meter cannot calculate the use-by period and you turn the meter
on to perform a test, the following symbols appear in the display:
34
Initial steps before testing