She leaves without saying goodbye
The engine learns each client's own visit rhythm and raises her only when her absence exceeds it. Someone who comes every four weeks and has been gone nine is a signal; someone who comes every twelve and has been gone nine is not.
Winning a new client costs several times what keeping one does, and leaving is silent — nothing in a diary announces that a regular has stopped appearing.
A client with fewer than the minimum number of visits gets no rhythm and no churn claim at all — she is classified as “no rhythm” and their number is declared. Two visits is one gap, and one gap is not a rhythm. The rhythm uses the median rather than the mean, so a single unusual absence — a trip, an illness — does not poison it.


