your English is okay, jorge. my first impression is that you should not be
adding together field values and saving that total into another field in a
table. that violates data normalization rules, and there's rarely a good
business or technical reason to do so. you must have some query, or
expression, or code, that you use to sum those different fields. standard
procedure is to use that whenever you need to calculate the sum and show it
in a form or report, whatever. that way the calculated value is always
current and accurate - you don't have to come up with some way to update a
table field at specified intervals.
if you're determined to save the calculated value into a table (which i
really, really do not recommend) then setting the value of the field back to
zero is as simple as running an Update query (see Help for details about
update queries, if you're not familiar with them). how to do it "once a
month only", can be more complex; it depends on whether you open the
database every day, or whether you're comfortable with scheduling a task to
open the database automatically to run the update...just how you go about
doing it depends on a lot of variables in both your database and the process
it serves.
hth
