Abbreviations are reused in different locales. PST in one locale can have different rules than PST in another locale. The reason the fully qualified name is needed is because it uniquely identifies a locale for which timezone rules can be followed.<p>Offsets aren&#x27;t always the right thing to use either. If you are in America&#x2F;Chicago and use -0600 for your timezone, that&#x27;s only accurate during standard time, and is off by an hour for daylight savings time. Knowing how&#x2F;when to shift offsets is part of the timezone rules associated with a locale, because they are not constant historically.