Accu-Chek performa Owner's Booklet page 54

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8. Press and release to set the level in
the meter.
9. " OK" and the control result alternate
on the display if the result is in range.
The range is printed on the test strip
container label. "Err" and the control
result alternate on the display if the
result is not in range. Remove the test
strip and discard it.