1) you need to take at least 20 or 50 samples in succession

You can start with 8 or 16. Or, heck, even just 2. Nothing stops you from varying the number of samples you average. You can start with just two and have a maximum of, say, 16 in your window.

And the "multiple sample" requirement doesn't change with the type of filter you use. You will need to average/filter several samples in order to stop the last bit from flickering.

Actually, if it's only the last bit that flickers, 4 samples should be enough to stop it from doing that, since you get an additional bit of precision for every 4:1 averaging step (so, 1 bit for 4:1, 2 bits for 16:1 and so on).

DSP, huh!, well the Fluke 45 uses the 6303 MCU, the Fluke 8840/42 uses the Z86-Zilog MCU, hardly DSP class processors?

Digital signal processing is, at first, a sub-discipline of mathematics and has exactly nothing to do with the processor you use. I've done digital signal processing on a '51, and I've done it on a TMS320VC54x. Both were adequate for the specific task.

And yes, averaging two samples is already digital signal processing.

Wow!, how about we start with a first order differential equation, you know, the one that actually governs the CR circuit universally?

Well, you were asking for how to get a stable signal, and not for a math lecture. I don't know if I could give the complete derivation from the top of my mind (start with the first-order differential equation, sidetrack into Laplace transformation, derive Z-transformation from Laplace transformation, arrive at a discrete time representation of the first-order differential equation). Also, if you're just looking at time-discrete signals, the step of deriving the Z-transformation from the Laplace-transformation might not be necessary to understand what's going on. In the book I linked to, even though it's _very_ heavy at math, the author explains the Z-transformation without deriving it from the Laplace one.