Glossary
Historical offset
Difference between local time and UTC that applied on the birth date. For Moscow on 12 April 1991 it was plus three hours, not the current value: the country cancelled and introduced time changes.
What it means
Historical offset — the time zone that was in effect at a specific location on a specific date, not today. Time‑zone boundaries and daylight‑saving rules have changed many times, and for dates of the past century the difference can be up to an hour. Example from platform checks: Moscow, April 1991 — correct offset UTC+3, not the usual UTC+4.
Where is this on the platform
Methodology