Four months after being announced, so-called “robotic umpires” have made their debut in baseball’s Atlantic League. The addition is one of several tweaks currently being piloted in the independent league in an attempt to update some fundamentals of America’s pastime.

The system utilizes TrackMan radar to determine whether a pitch is a ball or strike, a Doppler-based system that’s already in use at 30 Major League Baseball Stadiums and many more minor league parks. Information from the system is relayed to a human umpire via an iPhone and earpiece.

The system isn’t replacing home plate umpires entirely, and for now the human ump is required to monitor pitches as a kind of fail-safe. They can also ultimately override TrackMan’s calls. Among other things, the system isn’t set up to detect checked swings — when the batter stops a swing midway to let the ball pass.

“Until we can trust this system 100 percent,” umpire Brian deBrauwere said, “I still have to go back there with the intention of getting a pitch correct because if the system fails, it doesn’t pick a pitch up, or if it registers a pitch that’s a foot-and-a-half off the plate as a strike, I have to be prepared to correct that.”

Robo umps are one of a number of features currently being tested in the Atlantic League, with the intention of potentially bringing them to the majors, should things go well. Other changes include adjusting the mound’s distance from home plate and a three-batter minimum for pitchers.