PLM timeline
The life of the part in order: what happened to it, when, and on which project.
Open the part and go to the PLM tab. PLM stands for product lifecycle management.
What it is for
Everywhere else in the part details dialog shows you the current state: how much you hold, where it sits, what it costs. The timeline shows how it got there.
That makes it the tab to open when the current state is surprising. A quantity nobody can explain, stock in a location nobody remembers choosing, a part that went out and never came back.
Reading it
Events run in order, each against the project it belongs to. That lets you follow one part across several projects without losing track of which event belongs where.
Start here when a figure looks wrong
The instinct is to correct the number first. Read the timeline before you do, because a wrong figure is usually the visible end of something that went wrong earlier, and correcting it quietly hides the cause.
The timeline and cycle counts
A cycle count writes its correction here along with the reason code you gave. That is why the reason matters: months later this timeline is the only place the explanation survives.
A part whose timeline shows repeated corrections in the same direction has a process problem, not a counting problem.