Here's why:

* Balance Point: The fulcrum is the pivot point of the balance beam. It's where the beam rests and is free to rotate.

* Equal Distribution: The fulcrum's central location ensures that the balance beam is perfectly balanced when no weights are added. This allows for accurate measurement because any weight added on one side of the beam will cause a predictable rotation.

* Sensitivity: The fulcrum's position is crucial for the sensitivity of the balance. A central fulcrum allows for even the smallest differences in weight to be detected and measured.

Let me know if you have any other questions about triple beam balances!