I mentioned several times that people are free to pay more money and get this problem "fixed". Going on an on about it is like complaining that Ford Fiestas can't do 200mph. Technically true, but not going to make headline news or scandalize anybody.
But I expect the Ford Fiesta to operate as a car doing car things within its specifications. I do not expect the manufacturer of my car or DSO to lie or mislead about its capabilities. (1) Incidently, some cars like the Fiat Chrysler Jeep Grand Cherokee which killed Anton Yelchin fail this test because of poor human factors engineering; they are defective by design.
To give a single example (I could have picked from several), the Rigol does not support RMS measurements and it apparently never did even when it was working. I do not know what the automatic RMS measurement is measuring, but it is not the RMS value of the signal. To verify this, apply some Gaussian noise and measure the RMS value; it will be wrong. Now I know *why* the RMS measurement is broken but I only recently discovered it after becoming increasingly suspicious; the processing necessary to produce the display record corrupts the RMS value and measurements are made on the display record.
And it is not like digital RMS measurements are difficult; they are trivial. Calculate the standard deviation and you get the RMS value. The icing on the cake is that an *analog* oscilloscope can make this measurement to high accuracy. I expect my Ford Fiesta to carry my ESI 250DA impedance bridge as cargo just as well as other much older vehicles that I have used.
As I said, it honestly never occurred to me to look at a rise time without zooming in on the wave. Isn't it 100% natural to zoom in and look at the rising edge when you measure it? Make sure there's nothing weird there?
It is natural to do this for the very reason you identify; to know exactly what is being measured gives confidence in the measurement. Oscilloscopes are particularly useful tools in this respect.
On the other hand if the measurement changes when it should not, that undermines confidence. The DSOs I have used made accurate transition time and other measurements over a broad range of time/div and volt/div settings; if a weird result was produced, it was always because the signal was weird and not because of the instrument. They even tailored the number of significant digits reported to reflect the measurement precision.
Doesn't the Rigol position control shift the ground level? Position controls usually operate as offset controls with the position signal added before the digitizer. The difference is whether the signal is added before or after the attenuators.
Screenshot attached how it works on Rigol.
That does not really show me how the Rigol position controls work.
Position controls work over a specified number of graticule divisions. When the volt/div setting changes, the range of the position control in volts/div changes so the trace does not shift. If the position control operates by injecting a signal directly before the digitizer instead of only adjusting the display, then it serves as a very coarse offset control increasing the input range of the DSO.
Offset controls inject a signal earlier in the signal chain before some or all of the attenuation and gain stages. This increases the input range of the digitizer enormously which is important in some applications. In an extreme case like the Tektronix 7A13 differential comparator, the offset control can operate over a range of 20,000 divisions (it really operates like the display is 20,000 divisions tall) while the position control still operates only over 12 divisions of an 8 division display.
I think people would be complaining if the Rigol's position control did not inject an analog signal before the digitizer and only operated through the display because the limited input range would be a major problem. With a x10 probe yielding 50V/div, measuring the DC output of the input filter of an off-line switching power supply (340 volts DC) requires 7 divisions which is just within range of an 8 division oscilloscope (2) *if* the position control works as a fixed offset control. If the position control only changes how the signal is displayed, then the DSO would require 14 vertical divisions.
(1) Of course car manufactures do this all the time. That is why I hope to have nothing to do with GMC ever again.
(2) I am well acquainted with this measurement because with 1 or 2 very old exceptions, all of my analog and digital oscilloscopes have 8 vertical divisions and just barely make this measurement using only their position controls. I would be surprised if any DSO trying to stay out of the toy catagory cannot do this. Some of my oscilloscopes can make this measurement to very high precision and accuracy using their offset controls; a 7A13 can make a 340 volt DC measurement at 100mV/div.