Which instrument do scientists use to measure the mass of an object accurately?

The triple beam balance is the preferred instrument for measuring the mass of an object accurately because it utilizes a system of three beams with sliding weights, allowing for precise measurements. This device provides a mechanical advantage where the user can balance the object against known masses, thus allowing for exact readings down to small increments. Its design facilitates an accurate comparison of mass by balancing forces, making it suitable for laboratory settings where precision is crucial.

In contrast, a graduated cylinder is designed for measuring volume, a ruler is used for measuring length, and a thermometer is intended to measure temperature. Each of these instruments serves a specific purpose that does not pertain to the assessment of mass, emphasizing the unique function of the triple beam balance in scientific measurements of mass.