The name explains the micrometer clipers function, here is some history on it

"John Edison Sweet (October 21, 1832-May 8, 1916) was an American mechanical engineer who built the first micrometer caliper in 1873, for making tools, and who invented the “straight line” engine. He was a key founder of the American Society of Mechanical Engineers in 1880 and ASME’s third president (1884-85). Born in Pompey, New York, he died in Syracuse."

The advantage of the Venier Caliper is that it can measure not just inner distances but also outer distances with its two upper tines.