There isn't a single instrument specifically designed to "measure" gravitational force in the same way we measure, say, temperature or pressure. This is because gravitational force is fundamentally a force of attraction between objects with mass, and its strength depends on the masses of those objects and the distance between them.

However, we can indirectly measure the effects of gravitational force using various tools and techniques:

1. Measuring Mass and Distance:

* Scales: Scales are used to measure the mass of an object. The weight of an object (the force of gravity acting on it) is directly proportional to its mass.

* Measuring Tape/Rulers: These instruments are used to measure the distance between objects, which is another crucial factor in determining gravitational force.

2. Observing Gravitational Effects:

* Pendulums: Pendulums are used to study the acceleration due to gravity (g). The period of a pendulum's swing depends on the length of the pendulum and the local value of g.

* Accelerometers: These devices measure acceleration, which can be used to calculate the gravitational force acting on an object.

* Gravimeters: Gravimeters are specialized instruments designed to measure the local strength of gravity with high precision. They are used in geophysics, geology, and other fields.

3. Measuring Gravitational Waves:

* Laser Interferometer Gravitational-Wave Observatory (LIGO): LIGO is a complex network of observatories designed to detect ripples in spacetime called gravitational waves, which are generated by massive cosmic events like black hole collisions.

In summary, there isn't a single instrument that directly measures gravitational force. Instead, we rely on various techniques to measure the effects of gravity on objects or observe the behavior of gravitational waves.