Gravity might feel strong if you drop a bowling ball on your feet, but is in fact the weakest force. Compare it to electromagnetism: the pull of all the Earth’s gravity can’t stop you from picking up a paperclip with a refrigerator magnet. That weakness makes gravity incredibly difficult to measure.

A team of scientists in China are reporting that they have now performed the most precise measurement of gravity’s strength yet by measuring G, the Newtonian or universal gravitational constant. G relates the gravitational attraction between two objects to their masses and the distance between them. The new measurement is important both for high-powered atomic clocks as well as the study of the universe, earth science, or any kind of science that relies on gravity in some way.

The values measured by the team “have the smallest uncertainties reported until now,” according to the paper published in Nature.

Before we get to the experiments, a little more about what G is. Isaac Newton realized that gravity’s strength depends on the masses of two objects (like a planet and a moon) and weakens in proportion to the distance between those masses squared. But in order to calculate the actual gravitational force between two things, you have to multiply the combined masses divided by the distance squared by a very, very, very tiny number. Henry Cavendish first indirectly measured that number, G in the late 18th century.

Given how small it is, determining the true value of G is very difficult, and the agreed-upon value set by the international Committee on Data for Science and Technology (CODATA) is much less precise than the values agreed upon for other numbers that scientists use. Today, scientists use a value of .0000000000667408, give or take 47 parts-per-million. Essentially, calculating with this G is like trying to paint with a fat paint brush versus other experiments whose constants are like painting with skinnier paintbrushes.

In the new study, scientists performed two independent calculations of G using a pair of pendulums in a vacuum, one pendulum setup for each test. Each pendulum swings back and forth between a pair of massive objects whose positions can be adjusted.

The pendulums measure the force of gravity in two ways. First, they measure the difference between how quickly the pendulum swings to the “near,” or parallel position, versus the “far,” or horizontal position. They also measure how the direction of the pendulum’s swing changes based on the pull of the test masses.

Obviously, the experiments require super sensitive detectors and super well-controlled setups in order to determine accurate values for G. Each part must be specially fabricated and considered so the only possible force acting on the pendulum could come from the test masses. Additionally, the lab is in a special room in a cave to control for possible effects from changing temperatures.