Date/Time Calculations

I have a question about how Zoho interprets date and date/time fields, specifically in calculations.

For instance, if I have a date field (not a date/time field), is the date field actually a truncated version of the date/time field, or is it simply a date field?

For instance if the date field reads: 18-Jun-2009, does zoho really interpret this as 18-Jun-2009 00:00:00?

Thanks,

Leo