Most places have whole-hour timezone offsets Some places change timezones during the year One identifier can mean different zones:
PST: *P*acific *S*tandard *T*ime, *P*akistan *S*tandard *T*ime
EST: *E*astern *S*tandard *T*ime (USA), *E*astern *S*tandard *T*ime (Australia) and *E*astern Brazil *S*tandard *T*ime