Each row is a unit, each dot a cold or warm report. Rows are ordered so detected
riser groups sit together — vertical dot columns inside a group are correlated
outages. Within an event, the unit that consistently goes cold first is likely
closest to the fault.
0 riser group(s) detected in this range. Grouping comes from the
Risers analysis; ungrouped units may still share a riser — there just isn't enough
correlated data yet.