Analysis
Annotation
Also called chart note.
Annotation is a dated note pinned to a chart that says what happened on that day. It turns a bump on a line into a fact someone can read later.
How it is measured
An annotation is a date, a short text, and sometimes an author or a category such as release, campaign, or outage. It is stored beside the data, not inside it, so it never changes a count.
Keep them easy to find and easy to write. Add one when a deploy lands, a campaign starts, a tag changes, or a server goes down. Review the chart a month later and check whether every visible bump has a note beside it.
Worked example
A recipe blog sees a clean step up from 310 to 480 sessions a day starting on March 12. Nobody remembers why. Two weeks later a reader asks about a sudden drop on March 29, back to 330.
A teammate checks the notes and finds none. The sitemap was resubmitted on March 12 and the cache plugin was disabled on March 29. Both facts come from the server log, and now they sit on the chart for the next person.
How it differs
An annotation explains one date on one chart. A dashboard is the screen that holds many charts. The note adds context but no data; a dashboard adds data but not the reason.
Common errors
Writing notes only for big events. Putting the note in a chat thread instead of on the chart. Using vague text like 'changes'. Not recording tag and consent changes that alter counts. Deleting old ones.
In practice
Add a note for the last three things that shipped. From now on, make the note part of the release step. When a number looks strange, read the annotations before you open any report.