#The history timeline and rollback

Every operation is a node of the timeline. A model is not a picture but a recipe: the program walks the timeline top down and builds the result again.

#Everything else follows from that

• Go back to any step, change a number, and it rebuilds along with everything below.
• An edit to a sketch at the bottom of the timeline reaches the very last feature.
• A broken step is visible on its own line, not “somewhere in the model”.

#Rollback

The rollback bar temporarily stops the build at a chosen step: nothing below is built. That is how you look at what the body was halfway through, and how a new operation is inserted into the middle.

#Suppression

A suppressed feature is skipped but stays in the timeline. A modifier does not break the chain that way: suppress a fillet and the features below build on the body as it was before it. That is handy for variants and for finding the culprit when something fails.

#When a feature fails

Its line is marked and the reason appears in the status — as a code, not a guess: “the source body was not built”, “the cutting plane was deleted”, “the radius is too large for these edges”. Fix the named reason instead of rebuilding everything.

#See also

• The model tree — where that timeline lives.
• Parameters and formulas — what to change so everything rebuilds at once.