Daylight Savings Time (or DST)


Daylight Savings Time are seasonal time adjustments for economic and political reasons.

They are known as:

  • civil time
  • or daylight time

The Local time may change for political or economic reasons due to daylight.

They are political divisions of the earth's surface that allow the convention that time is measured the same at all locations within the time zone, regardless of the precise value of sun time at specific locations.


The time zone Europe/London is:

  • in standard GMT / UTC: UTC+0
  • but in DST known as the British Summer Time (BST): UTC+1

Rules / History

The rules are stored in the timezone databases.

The zone and rule lines reflect the history of DST.


# Rule  NAME    FROM    TO      TYPE    IN      ON      AT      SAVE    LETTER/S
Rule    US      1918    1919    -       Mar     lastSun 2:00    1:00    D
Rule    US      1918    1919    -       Oct     lastSun 2:00    0       S

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