Assign webix.DataRecord with webix.form

I need implement in my model calculated fields: start-date, end-date and count-day. When I change start or end I’d like calculate days. But when I try assign DataRecord with form methods. setValues, or bind
I can not keep track of which field changes in DataRecord.onChange or form.onChange.

Ok. I myself have found a solution.
To find out what specific fields of the form have changed, use the following code. http://webix.com/snippet/b4d64f08