I find DC measurement errors min +1% max +10%. Max error happens about 5 V. I already tried recalibration. Is it OK?
Make sure the range is suited for the measurement you are performing, e.g., do not measure 200mV on a 10V/div setting.
Make sure DC reference is properly set before attempting any DC measurement (Set unit in auto range, set input coupling to GND and wait a couple of seconds).
If the unit is still not measuring correct, return unit for inspection/adjustment/repair.