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Tick data usually carries a timestamp. Some sets round to the second, others show milliseconds. The difference matters for ordering events.

With second-level timestamps, a burst of 20 ticks within one second all share the same time. The order within that second is preserved only by the file's sequence, if at all. When the data gets merged with other sources, such as another pair or a news timestamp, ties arise and the ordering is arbitrary.

For a strategy that reacts to a news release at 8:30:00, whether the first price change came before or after the official time can't be told with second precision.

Millisecond data solves many of these problems but creates others: the broker's server stamps each tick with its own clock, and the client receives it later. The time on the tick isn't the time the client saw it.

Microsecond precision exists in some professional data. For retail work, milliseconds are generally enough, provided the clocks involved are synchronized.

Before analyzing timing questions, check the resolution of the data and ask whether the answer depends on it.

Platforms differ here. MT5 records tick times in milliseconds, MT4 mostly in seconds. Third-party feeds sometimes offer microseconds. The resolution available should match the question being asked, and no finer.

What precision does your tick data provide, and has it ever limited an analysis?

My first tick files came from an old MT4 export and they only had whole seconds on them. I didn't notice it was a problem until I tried to measure how fast EURUSD reacted to the US jobs number. Every release showed the first move in the same second as the announcement, so my spreadsheet claimed the reaction was instant, which told me nothing at all.

When I moved to MT5 and started saving ticks with milliseconds, the picture changed. Most releases showed a short pause of a few hundred milliseconds and then a burst, and sometimes the quote actually twitched slightly before the official time, which I put down to clock differences rather than anything sinister.

The thing I learned the hard way is to sync the PC clock before trusting any of it. Mine had drifted almost a full second over a couple of weeks. These days I run a time sync tool in the background and note the offset in my log before each news session.