How to subtract date from date without using excel or any other program

Common sense way of subtracting 2 dates. At many places students are required to compute number of days, months and years between 2 dates. For example in computing exemption of gratuity duration of service is required. I have seen student calculating duration of service in fingers. It is time consuming and mistake prone. Therefore to make it easy I teach them how to subtract 2 dates. Similarly in computing leave salary, sale of movable assets etc there is a requirement of subtraction of dates. I hope students will like my small efforts. Your encouragement and kindness always welcome. thanks for watching this video patiently.