I am trying to do this :

UPDATE Projet SET DateMaximum='2021-07-31 23:59:59.999' WHERE ID=1

I discovered that SQL Server saves it as 2021-08-01 00:00:00.000.

If I use 998 milliseconds, it saves it as 2021-07-31 23:59:59.997'.

All other values are working.

Why it is that 998 and 999 milliseconds cause such a reactiom?