Calenculator is a tiny utilite to count the diffirence in days between two dates. It's realy small and light and consists of less than one hundred lines of code.
1. Today you start to attend some courses which last for 60 days. So you input the courses start day into the left calendar widget, 60 days difference into the "Difference in days" spinbox, you will see the result of calculations in the right calendar immediately.
2. You stoped smoking at the 7th of August, today is the 17 of December. How many days you didn't smoke. Input the dates in calendar widgets and see the difference in the "Difference in days" spinbox.
3. You compose your trip programme. So the first day is depature from London and arriving to Moscow. The second day you spend in Moscow. The third day you depart to Saint Petersburg. You are going to stay there for a week. So if this day is the 3rd, then (type 7 into "Difference in days" spinbox), then look at the right spinbox (then this day is #).
It's really easy to use and intuitive utility. Sometimes it's just more convenient to have two calendars before your eyes at a moment.