Rebuild .003 then .005 worse now .8 then .01 whats going on?

Having seen rebuild alter a curves accurate path I am a little cautious of this command. I have a curve with 19 points, it was 13 until adding a required extension either end for surfacing before trimming it back down to original length.
I select the curve, run rebuild to just consider it and I note the deviation 0.003, and decide not to run it, then revisit it within a minute or so and consider it again as 0.003 I decide is ok, yet this time it says 0.005, same settings as before.

is this normal ?


Hope to hear what is going on with rebuild tool here. When starting out with rhino my first ever use of rebuild saw it alter a curve more than I dare let it as that then messed up the aerofoil section more than was suitable.

Following a revisit to this tool only to spot two different deviations on the same curve. and the start of this post,…

I have now a much more worrying occurrence, yet try again and sanity returns.

first time it declares 0.8mm change to my profile, now as you can see thats a drastic change, this wouldnt fly !
try again a while later and only 0.01 and no alarming curve shift.

I have come back to having to consider rebuild as its right and proper to sweep curves with same control points.

I have one curve with 42, another it says segment 1 control point 5 segment 2 has 6 and so on.

so either a case of adding them all up to see what I have or rebuild it.

I have worked my way through all my curves using 13 and 3, so as to sweep them.

see attached
Rebuild sees two very diffferent deviations same curve.3dm (32.8 KB)