>Unlike dates, datetime is stored as a double. I hit this sometime ago too and discussed here. If hour portion is not a multiple of 3 then roundation problems occur.

From my understanding, it's not strictly a double, it's actually 2 integers. DateTime is stored in 8 bytes, the first 4 bytes are in integer date, offset from 1/1/100, the remaining 4 bytes are the time in milliseconds since midnight (If I'm wrong, I know I'll be shot down in flames, regardless of how close to Christmas & the season of goodwill, I'm quoting from VfP 5 help here, which has exactly the same problem).

If this is the case, then any difference cannot really be explained as rounding error. And even if rounding error, why a difference of multiples of exactly 3 hours (180000 mS) should have no rounding error.

Paul