An account's own normal level for a measure, usually the median over a trailing window of twelve weeks or months. Surges and silences are measured against it, not against a global figure.
The baseline is the account's own history. The norm is what similar accounts do. A surge is against the baseline; a gap is against the norm.
Too short and normal fluctuation becomes a surge. Twelve periods is the usual floor.
The median of the account's own values over a trailing window, usually twelve weeks or twelve months, excluding the current period. A movement is judged against this, not against other accounts.
An account's weekly orders over twelve weeks have a median of $8,200. This week it ordered $3,100, 38 percent of baseline. Another account at $3,100 has a baseline of $2,900 and is fine.
Using the mean, which one unusual order drags. Or using a baseline so long that a customer who changed a year ago is still compared with what it used to be.