His phone clock was four minutes fast. The chat broke.

transcript

Rohan's phone clock is four minutes fast. That's all it took to scramble a group chat about money.

On Meera's laptop, Rohan's reply says: done! Done what? It sits above the very payment request it answers.

The app sorted by the sender's clock. Rohan's says he answered first. But every phone's clock is a little wrong. So devices can even disagree.

The fix: every conversation gets one owner. It hands out numbers. Priya's request arrives first. It becomes 412. Rohan's reply comes next. It becomes 413. His clock doesn't matter anymore.

Bonus. Numbers make gaps visible. Timestamps never could. Got 410, then 412? Go fetch 411.

But here's the catch. What if the owner dies? The new one starts from the last stored number. A unique key blocks the old one from reusing it.

Never trust a phone's clock for order. Trust one owner's counter. One, two, three.

Full breakdown in the lecture.