What was the primary invention that Blaise Pascal is known for?

Blaise Pascal is primarily known for inventing the first adding machine, which he created in the 17th century. This device, often referred to as the Pascaline, was designed to perform addition and subtraction directly. It used a series of gears and wheels, allowing users to input numbers via dials and receive a printed output of the result. Pascal's invention is significant because it laid the groundwork for the development of mechanical calculators, influencing future advancements in computing technologies.

The other choices, such as the first programmable computer, first digital computer, and first mechanical calculator, refer to later inventions and developments that followed Pascal’s time. While later figures like Charles Babbage and Alan Turing contributed crucially to the fields of computing and programming, Pascal's work specifically is recognized as a pioneering milestone in the realm of calculating machines.