On-board data handling is like a computer in a vehicle or a machine. Just like how you use a computer to do tasks and play games, the vehicle or machine uses a computer to do tasks and make decisions about what to do next. The computer takes in information from sensors like how fast the vehicle is going or if the machine is overheating, and then it makes decisions based on that information.
For example, if the vehicle senses that a person is walking in front of it, the computer will tell the brakes to stop the vehicle so it doesn't hit the person. Or if the machine is working too hard, the computer will tell it to slow down or take a break so it doesn't get damaged.
The on-board data handling computer is like the brain of the vehicle or machine. It helps to keep them safe and working properly.