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[Reply #15 on:]

all the averages, diff to diff, running averages, serial second derivitive?  head spinning!!!

:-)

If your data is all coming in the same then there would be no difference between data points, right?

If the data is getting larger then the difference between data points, the last one subtracted from the one before, would be more than zero.

Example:
data: difference, difference-of-difference
1 ............ no data before this to subtract from this so no difference or difference-of-difference
2: 1 ......... we see the data is increasing by 1. but no difference before this so no difference-of-difference
4: 2, 1 ...... we see the data increasing by 2 and we see that the increase is increasing by 1
7: 3, 1
12: 5, 2 ..... we see the increase is increasing by 2
16: 4, -1 .... we see the data increasing by 2 but now that increase is getting to be less
19: 3, -1 .... data still increasing but not as fast as before
21: 2, -1 .... if we drew a curve of the data it would still be going up but starting to 'hilltop'.
22: 1, -1
22: 0, -1 .... and here the data curve would be level
20: -2, -2 ... then it's going down

The difference is like rate of change of the data, +values are increasing and -values are decreasing.
The difference-of-difference is like the rate that the difference itself is changing.
If the data is not chaotic then the diff-of-diff (just abbreviating!) will tell you the trend farther ahead than just the difference will do.

By using the difference and difference-of-difference you can detect two levels of change to spot trends. You can take that as many levels as you want btw, but remember that the time between data points needs to be (at least close to) even for it to work.
 
Sorry about the terms, they aren't exactly standard and the approach is a bit rough. I just took an idea from calculus and applied it to data, have done so before to good ends even though it's not precisely calculus.

[Reply #16 on:]

I have to repeat my question: what is it that you are after?

[Reply #17 on:]

I have to repeat my question: what is it that you are after?

I am after illumination, as to what the logic of a simple sketch would be to accomplish the example I described two posts ago...

I did not think that something like this would be so difficult to understand, nor that folks would be willing to provide so much lecturing, as to how to eat, sleep, think, and go about life.....other than an example as to how it might be done!

LOL!!

[Reply #18 on:]

(BTW, I'm a ShopBot owner - and I also have designed and built my own CNC router. I like the looks of your Stinger.)

NICE!! A shopbot is a very nice machine, and I was actually considering it before building mine...however the somewhat "proprietary" control and software did not exactly appeal to me...I know folks driving them with mach3, and the machines are absolutely fantastic!

I am considering adding a fourth axis on mine, currently designing it solidworks as well, and we will see how that goes.  Have been very happy with my design, it's rigidity, speed, and precision.  If I was going to do it again, I would make the sides stiffer, this way I would be able to cut light metals, but for wood, so far the machine has performed beyond my wildest expectations!

Any video of your "home-made" machine?

[Reply #19 on:]

The home-brew machine is a 3½-axis (spindle can be locked anywhere from vertical to horizontal) with a 1/4800" step size. My only images are stills I took during the build/test stage. I've posted three of the stills in the thread at http://arduino.cc/forum/index.php/topic,88204.0.html (Bar Sport, where stuff like this is topical).

More topical: If you have difficulty converting data points to a function, do a forum search on "least squares" - a while back I posted C source for a program (FABLS.c) that fits linear and a number of non-linear functions. It may help.