Digital marketing is a subdiscipline of marketing, which uses digital technologies, predominantly on the Internet, but also including display advertising, hand-held and mobile devices and all other digital media to market products or services.

According to Wikipedia: A calculator is a machine that allows people to do math operations more efficiently. For example, many calculators will add, subtract, multiply, and divide. Some also calculate square roots, and more complex calculators can help with calculus and draw function graphs. Calculators are ubiquitous. Smartphones and other computers can also serve as a calculator.

Some calculators, such as the abacus, will work without requiring batteries. Others, like the electronic calculator, need batteries. There are two main types of electronic calculators: simple calculators—which can only add, subtract, multiply and divide, and sometimes take square roots—and scientific calculators—which can do many other things, such as calculate factorials and trigonometry functions.