The same clock time can mean different charts
A birth time recorded in Hong Kong, London or New York sits inside different time-zone histories. Birthplace helps the calculator handle that context.
Daylight-saving rules complicate memory
Some locations used daylight saving in certain years. If a calculator ignores this, boundary-sensitive charts may shift incorrectly.
Accuracy is especially important near midnight
Near midnight, a small time-zone issue can affect the day pillar. Since the Day Master comes from the day pillar, this can change the whole reading.