I recall the 10 o'clock whistles at the old Shell complex at the town area. This whistle will go off every Thursdays at 10 o'clock mornings in those good old days.
I've never figured out what the whistle was for, but every time when it goes off, this either intentionally, or unintentionally prompts everyone to check their watches and reset the time if necessary. I'm not sure if this was a timekeeping thing, but it sure is handy for that purpose. This whistle kept up until the early 1980s long after the refinery was moved to Lutong and it fell silent after that around that time.