> I never saw a need for this in HFT. In my experience, GPS was used instead, but there was never any critical need for microsecond accuracy in live systems.

mifid ii (uk/eu) minimum is 1us granularity

https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=uriserv:...

It's 1 us granularity, which means you should report your timestamps with six figures after the decimal point.

The required accuracy (Tables 1 and 2 in that document) is 100 us or 1000 us depending on the system.

> The required accuracy (Tables 1 and 2 in that document)

no, Tables 1 and 2 say divergence, not accuracy

accuracy is a mix of both granularity and divergence

regardless, your statement before:

> The regulatory requirement you linked (and other typical requirements from regulators) allows a tolerance of one second, so it doesn't call for this kind of technology.

is not true

> accuracy is a mix of both granularity and divergence

I respectfully disagree.

In context, "granularity" is nothing more than a resolution constraint on reported timestamps. Its inclusion adjacent to the specified "divergence from UTC" is a function of market manipulation surveillance objectives as discussed in preamble item (2), and really doesn't have anything to do with accuracy proper.

any time i am certain of something i never capitalize and i do not end my sentences with periods or use any punctuation because i like people to believe i am an omniscient narrator who cannot be interrupted

> mifid ii (uk/eu) minimum is 1us granularity

1us is nothing special for GPS/NTP/PTP appliances (especially with OCXO/rubidium oscillators):

* https://www.microchip.com/en-us/products/clock-and-timing/sy...

* https://www.meinbergglobal.com/english/productinfo/gps-time-...