The blue Parachrom hairspring inside Rolex movements gets all the attention. Its anti-magnetic property keeps our watches ticking with accuracy when they happened to be placed near magnetic fields such as those produced by loudspeakers, refrigerators, some handbag or tablet case clasps.
But the overlooked component that is key to the legendary precision of Rolex timepieces lies nearby: the balance wheel.
The Parachrom hairspring and the balance wheel work together. They are tied at the hip, or rather mounted on one another. The hairspring could not beat its hypnotic rhythm without the inertia effect produced by the balance wheel. Together, they're truly the heartbeat of a Rolex watch.
Photo credit: Rolex
The balance wheels are machined from solid bars of copper-beryllium alloy at the Rolex Bienne site. In Rolex labs, copper-beryllium is said, in French, “cuivre beryllium,” and abbreviated "CuBe," the same as on the periodic table. CuBe has some anti-thermal, anti-magnetic properties.
But Rolex engineers have recently made a discovery. When they switched the alloy from CuBe to an alloy that has more insulator properties — an alloy less conductive to electricity — they could increase the anti-magnetic rating of the watch beyond what they’ve ever been able to.
"Surprisingly and unexpectedly, increasing the resistivity for a metallic material is very important in the increase of the magnetic threshold,” Rolex wrote in its patent filing with the Swiss Institute of Intellectual Property.
“An increase of several orders of magnitude in the resistivity (by the use of insulating materials) will in all likelihood make it possible to further increase the magnetic field threshold.”
Rolex engineers in their tests took a superconducting electromagnet that created a magnetic field with intensities of the order of 10 tesla, or 100,000 gauss, and cranked up the power. They exposed the watch for 20 minutes in each setting, 0.25 tesla at a time.
In the current configuration, with balance wheels made with CuBe, Rolex watches were able to sustain between 22,500 gauss and 25,000 gauss, which is nothing to sneeze it.
(There is no official information regarding the anti-magnetic rating of Rolex watches today. But the control testing published in the patent has finally provided us with a clue.)
Source: Rolex via IPI.ch
In the second series of tests, Rolex used balance wheels made out of lead-free brass, something they’ve called “Ecobrass.” And that's when Rolex engineers were amazed.
“Changing the material of the balance wheel had an unexpected and surprising effect. […] Lead-free brass has a higher resistivity than the CuBe commonly used for balances and plates,” the patent read.
The tests revealed Rolex engineers were able to crank up the power to 4 tesla, or 40,000 gauss, before seeing any adverse effects on the timing of the watch . “The only threshold in this configuration was observed after exposure to 4 T,” said the patent, using the tesla unit. “Which is absolutely remarkable.”
It's unclear if these innovations will find their ways to Watches and Wonders in 2024. The Milgauss line was discontinued a year ago. With today’s advances in horology, all Rolex watches are anti-magnetic to more than 1,000 gauss, which put a question mark on the Milgauss' raison d'être.
“Honouring science” was Rolex’s most recent tagline for the Milgauss up until the day it was discontinued, a reference to its long-term association with Geneva-based Conseil Européen pour la Recherche Nucléaire, or CERN. Rolex has not given up its relationship with CERN, which is still featured prominently on rolex.org.
But one thing for sure, Rolex’s innovative spirit will make the brand untouchable when it comes to anti-magnetic property — and will resurrect hopefully the historic Milgauss line.