Hi all.
So again I am following an infinite skills tutorial to build a razor.
I am following along and twice now the history command has been broken when in the tutorial they haven’t.
The first time was doing a boolean difference and the second time was joining to curves.
My problem being in the video they join the curves and then extrude along a curve and then use the history to tweak the original joined curves.
Which I can’t do now ?
The tutorial is in rhino for windows ?
Many thanks
Glenn
Hi Glenn,
Do you mean the “Cutting Out The Body” video from infinite skills tutorial?
Hi Mohammad.
Yes thats the tutorial.
It seems most commands i’m doing are breaking the history but not in the tutorial.
Although one of the commands still worked so i’m thinking maybe It’s me not quite understanding how the history command works 
Hi Glenn - The rulles are pretty simple for History in Rhino- if everything is working as it ought to. then
This is not true of edits to children that modify attributes like layer, color, material etc, but a Join output curves would break history.
Commands that can have multiple input objects like FlowAlongSrf, or Loft, or Sweep2 allow edits to any of the inputs .
Does that correspond to the breakage you’re seeing?
-Pascal
Pascal gave full answer! 
But in the video there is no history after join 2 curves. instead same points from both joined curves selected and scaled using gumball. That’s act like history in mirror!
Mohammad Nikookar
So by that would I be right in thinking that …
A curve would be the input/parent.
An extruded surface from that curve would be the output geometry / child.
If I modified the curve/parent then the surface/child would change to match.
Then as soon as I modify the surface / child thats breaks the history command and any alteration to the input/parent then has no affect on the output/ child.
Cheers
Archie.
Cheer’s Mohammad !