Ruben T. from Stavanger, Rogaland, Norway asks:
Hi, I am looking into the world of watches and probably intend on buying one in the coming few years. I want to wear it every day without worrying too much. On various blogs, forums, websites I read that magnetic field are probably a watch's worst enemy, mainly due to them being invisible. Several watch companies (Omega, Rolex, IWC, Vacheron Constantin) offer models with some sort of protection against magnetic fields.
Here comes the first problem. Different units are being used in describing the level of protection. IWC, Omega, Rolex all use the Gauss, where 1000 Gauss is approximately equal to 0,1 Tesla. Vacheron Constantin (The overseas model) uses the Ampere/meter. How are these different units related and why do they use different units?
Second question is how much protection is actually needed for everyday life? Omega offers up to 15,000 Gauss protection. I experienced what a magnet of this size can do and what it looks like. It seems VERY unlikely that one encounters this in daily life and those who do are probably wise enough to take of their watches before coming close to the magnet.
How likely are timepieces without protection to become deregulated?
It is true that the type of magnetic fields which the Omega 15,000 Gauss watch can protect against are highly unlikely to be encountered by normal people on a regular basis. If you work with MRI machine or at CERN you might be among those who are the exception.
Magnetic fields are all around us, but most are too weak to really interfere with your mechanical watch. The real issue is that if they do, they can cause a lot of problems and force your watch to be serviced for demagnetization by a watchmaker.
So, what are some types of instances to protect against? Avoid playing with neodymium magnets, avoid de-gaussing video or audio tapes, don't stick your watch on the magnetic clasp of a lady's handbag. For the most part, it seems unlikely that watches are subject to medium or high intensity magnetic fields in the course of most wearers' daily lives, forces that would penetrate the steel case, the dial, and the steel caseback. Of course, if you have a skeleton dial and crystal caseback, there may be a potentially higher risk of magnetism-related watch movement damage.
A lower magnetic field can cause a watch to run fast, but return to normal operation after exposure subsides. A medium intensity field can cause a watch to run fast permanently until service restores functionality. A high intensity field can stop a watch. Like we said, proper service that demagnetizes the components will cause the regulation and amplitude to return to normal. If you are worried or like the idea of a highly anti-magnetic timepieces, they can't hurt and do make for fine watches.
The other part of your question is related to how they measure magnetism and their relative resistances. Prepare to geek out:
Gauss is a unit of magnetic induction. As a unit of measure, it's been formally superseded by the Tesla as a unit. The ampere, or amp, describes the electromagnetic field in this context. Normally, amps are a measurement of electrical current.
10,000 Gauss = 1 Tesla. Further, 1 amp / meter = 4(3.14) (1000) Oersted, or 12560 Oersted.
Now we need to relate Oersted to Tesla. The problem is, they're measuring different qualities of the magnetic incidence. Tesla or Gauss is the unit of magnetic flux density B, while the ampere or Oersted is the unit of magnetizing field H.
Flux density is the number of magnetic lines passing through a surface placed in a magnetic field. The unit of magnetizing field is about measuring the strength.
Really what we're trying to get down to here is, the shape of the field, the strength, and the permeability. These two different measures interrelate in a formula that describes the permeability and how much force is needed, usually measured in Newtons.