i tried this on my database to calculate the difference between onblock and 
offblock but i got "00:00: answer.  I am using QUERY to calculate the time. 
on my table the onblock and offblock was formated as SHORT TIME.

 DateDiff("n",Format([onblock],"Short Time"),Format([offblock],"Short Time"))

Please help. . .

Drop the Format(). The function outputs the Text type, which then has to be 
converted back into Date/Time type, and there's opportunities for errors.

Just use:
    DateDiff("n", [onblock], [offblock])

This might also help:
    Calculating elapsed time
at:
    http://allenbrowne.com/casu-13.html

-- 
Allen Browne - Microsoft MVP.  Perth, Western Australia
Tips for Access users - http://allenbrowne.com/tips.html
Reply to group, rather than allenbrowne at mvps dot org.

"jor" <jor@discussions.microsoft.com> wrote in message
news:1FA41571-64FA-4693-AB84-F7103E907E84@microsoft.com...
>i tried this on my database to calculate the difference between onblock and
> offblock but i got "00:00: answer.  I am using QUERY to calculate the 
> time.
> on my table the onblock and offblock was formated as SHORT TIME.
>
> DateDiff("n",Format([onblock],"Short Time"),Format([offblock],"Short 
> Time"))
>
> Please help. . .