#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. Drag the bar up or down, or pick Roll back to here from the right-button menu of a row; Clear the rollback in the same menu builds the whole timeline again.

#Suppression

A suppressed feature is skipped but stays in the timeline: the right button on the row -> Suppress, and Enable to bring it back. 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 row turns red and the reason is said in words: “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.

#Deleting a line

Select the line and press Delete. The window shows what is built on it. Only the line itself goes: what is built on it stays in the timeline, red, with the reason “what it was built on is deleted”, to be repaired or deleted. To remove it all at once, tick “Delete what is built on it too”. Changed your mind — Ctrl+Z brings everything back.

#See also

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