Getting the birth time right: zones, coordinates and summer time
A contributed chart is only as good as its time, and most errors in birth data are not in the clock reading. They are in the zone.
Give us the time as recorded
Send the time exactly as the document states it, together with the place and the source. Do not convert it yourself. Conversion is where errors enter, and we would rather do it once, consistently, with a record of what was applied.
The three things that go wrong
The zone in force at the time, not the zone in force now. Zones have changed, in some countries repeatedly. A birth in the 1970s may fall under a different offset from the same place today.
Summer time. The commonest single error, and it is worth an hour of the chart — enough to move the Ascendant by up to a whole sign. Whether summer time applied on a given date in a given country is a matter of record, and the record is not always what people remember.
Coordinates. The birthplace itself, not the nearest large city. A few tenths of a degree matter little for the planets and can matter for the Ascendant, especially at high latitudes.
A note on the sign convention
Eastern longitudes generally take positive offsets from Greenwich, western longitudes negative ones. The sign is reversed in some older astrological software, which is a durable source of charts that are off by exactly twice the offset. If a chart looks wrong by a suspiciously round number of hours, this is the first thing to check.
Where to check
Historical time zone and summer time data for almost any place and date is available from the standard online ephemeris services, which list the offset actually applied for the date you enter. A geographical atlas gives the coordinates.
If you are unsure, send what the document says and tell us what you are unsure about. An honest uncertainty is usable; a confident conversion that turns out to be wrong is not.