Thank you PJ2 for the excellent reminder about the vagaries of data collection and an interesting presentation of the concept.
Just because a point is plotted on a DFDR chart does not mean it is not an interpolated or smoothed point seems to be a key element of your message.
There is one more factor to be considered in analyzing flight control data. The maximum uncertainty of position for those items that are moving (such as control surfaces and actual controls). Real objects move at characteristic rates. A control stick will not move from full left to full right in a millisecond. Even if it could, and then immediately returned to its original position, could a hydraulically driven control surface follow such a short signal?
Suppose a rudder surface takes a full second to go from neutral to full right at maximum control input. If sampled 4 times a second, you may not know exactly when it reaches maximum deflection or exactly when it reversed its direction of motion, but you can still know it moved at close to its maximum rate and achieved approximately full travel. Estimates can be made for the uncertainty and approximate behavior determined.
The AA587 investigation had real problems with the DFDR data because the low sampling rates masked the dynamic nature of the oscillations. Lets hope that more rapid sampling rate recorders were mandated as a consequence.
If data is recovered from AF447's recorders, will the sampling rates be high enough to definitively show dynamic behavior of the aircraft and its controls? Let us hope so.
Meanwhile, does anyone have knowledge of the sampling rates on the Air Canada A319 aircraft we were just discussing?