Percentage tolerances are specified by all manufacturers of meters & test strips for results.
Check that immediate sequential tests from the same large drop of blood are within the percentage allowed for that particular meter. If not, try new pot of test strips. No improvement..? then it's time for a call to the manufacturer - replacement of the meter.
It clearly states in the micro-print of the user guide in each strip box that no major clinical decisions must be taken from a single strip test. It follows that several will give you an average to determine your state of BG health at that particular point in time.
Carpe diem.