Data engineering·Governance, privacy and meaning
the same metric name means something slightly different than it did in March, and the year-on-year chart is comparing two definitions.
Metric drift
Also calleddefinition drift, metric divergence
A measure's definition changing over time without the change being versioned or announced. It is uniquely damaging because it corrupts comparisons rather than values: every number is correct on the day it was computed and the trend between them is meaningless. Versioning definitions and recording when each took effect is the only durable fix, since restating history is often impossible.