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Why are oscilloscopes so inaccurate?
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magic:
You will sooner reach limitations of the scope than the probe.

Particularly at DC. Scope probes are actually usable with DMMs in a pinch if you calibrate them beforehand. I did it once to measure something that needed not to be disturbed by extra capacitance and noise, though I was only after 1% or so accuracy.

A scope I wouldn't trust to get even 1% right.
tggzzz:

--- Quote from: magic on August 28, 2019, 12:02:28 pm ---You will sooner reach limitations of the scope than the probe.

--- End quote ---

DC voltage maybe, maybe not.

Otherwise poor probing technique frequently dominates measurement validity.
SilverSolder:
Playing around with a ratio transformer the other day, I decided to check a 54622D scope, just for fun.  Fed an accurately sourced 1V rms signal at 50Hz via a 10:1 probe, the Agilent was able to achieve ~0.7% accuracy on the calculated RMS value it displayed on the screen. 

This level of accuracy (better than the spec of 2%) was only achieved right after running the self calibration function.  The accuracy was a lot worse before running user cal - several percent out!

Overall better than expected performance, and a good demonstration of the value of the Auto Cal function.
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