Re: Calibration of oscilloscope doesnt make it accurate?
Some assumptions in this thread are wrong. Modern oscilloscopes have various kinds of internal gain and waveform adjustments, mostly performed in the digital domain. Many of it are already modified in self-calibration procedures, e.g. with a loop-back cable connection from test signal output to signal inputs.
In practice, it's unlikely that a digital oscilloscope fails the relative wide level accuracy specifications (e.g. +/- 2 %)without an actual defect. If this happens, the fault should be normally detected in calibration. There's a certain possibility that not all vertical attenuator settings are calibrated so that a defect isn't noticed.
A calibration protocol worth it's name will always indicate which settings have been checked against which specification.
On the other hand, it's relative easy to perform your own calibration check for the range of interest.
If I would bet, there's a 95% chance of an inappropriate measurement setup and 5% of a faulty calibration.