I have a Boolean variable stored in Odoo (OpenERP) database, I want to display it's values according to time axis, every minute.

I tried to do this with "interval" attribute in a graph view in xml but the graph regroups all true values and display the sum of them, so if have 5 true values at 13:05, it will display the graph rising to the value "5" instead of "1" in this minute.

Is there a better way to do this ?