Calculate your overtime or undertime: just enter the 'From' date and time, and the 'To' date and time and walah! the number of hours and minutes worked is calculated. Click on the plus (+) button to add this to a list that's saved.
At the list view, enter your regular working hours and your overtime or undertime are calculated.
To see the list without adding to it from the startup screen, just click the middle CalcList button.