Saigonauticon , 7 months ago

A pocketwatch manufactured in 1889. I keep it running as a memento mori: the watch may outlive the watchmaker. Build things well – they may be all people remember you by, one day.

I also have a slide rule at my desk at most times, to remind me of false-precision.

I guess the oldest though, is a Wu Zhu coin from the Three Kingdoms period (currency is a technology, too?). I keep it to remember that all empires arise from chaos, and must return to it; that all assets eventually have no value. That the things that endure, are stranger currencies still.