anti-magnetic issues (and your watch)

 an old saying is something like "knows just enough to be dangerous" ...

One of the things that the King Wang New Watch Purchaser today seems to fuss about is accuracy, its pretty common for the new watch owner to expect that their new object of fascination should be accurate to within seconds per day (and they'll check every day). Especially young people who grew up in the age of cheap quartz timed movements (which nearly toppled the entire mechanical watch industry) imagining that their $500 watch "must" be more accurate than a $20 one. That boys and girls is why Quartz nearly killed Mechanical.

One of the things which emerges quickly is it's not up to Swiss Chronometer standard, and Google "my watch is [slow | fast]" and may find a suggestion that the cause is "your watch has been magnetised" ... frankly I'm of the view that 90% of the population don't have the faintest idea what magentism even means.

So if you're wondering if your watch is running fast or slow because its been magnetised then the first thing you should do is look for this symbol on your watch

That symbol tells you that the watch is resistant to being magnetised. In the case of Seiko it goes like this:

Seiko case back markings

1. No inverted U indication: certified level of anti-magnetism: 1,600 A/m. Your watch will not be affected by the level of magnetism that ordinary watches can withstand.
2. Inverted U with 1 bar (Type 1): certified level of anti-magnetism: 4,800 A/m. Your watch will not be affected by the magnetism generated by household appliances at a distance down to 5cm.
3. Inverted U with 2 bar (Type 2): certified level of anti-magnetism: 16,000 A/m. Your watch will not be affected by the magnetism generated by household appliances at a distance down to 1cm.

Now the normal standard for Japan made stuff (and that means the movement) is that its like this

Magnetic resistance performance

Type	Magnetism resistance (in case of direct current magnetic field)	Explanation
Common timepiece	Up to 1,600 A/m (approx. 20 gauss)	The minimum magnetism resistance requirement for a watch. (For reference)
Type 1 antimagnetic watch (magnetic resistant watch)	Up to 4,800 A/m (approx. 60 gauss)	A magnetic resistant watch almost always maintains its performance when placed at 5 cm from magnetic field generating devices of everyday life.
Type 2 antimagnetic watch (super magnetic resistant watch)	Up to 16,000 A/m (approx. 200 gauss)	A super magnetic resistant watch almost always maintains its performance when placed at 1 cm from magnetic field generating devices of everyday life.
Diver's watch	Up to 4,800 A/m (approx. 60 gauss)	The magnetism resistance requirement for a diver's watch.

• Type 1 and 2 requirements are defined in JIS B 7024 - Magnetic resistant watches, and diver's watch requirements in JIS B 7023 - Divers' watches - Classification and performance.
  
• Generally, resistance of watches is indicated according to the old JIS B 7024 standard, but indications are now being changed for the current ISO standards.

referencing this site.

So what does this A/m and gauss mean?

Well like most things there is a measurement for it, like how much water is in a bucket, how fast you're going ... magnetic field strength has a measurement too it is Gauss.

Now for non metric users (those who are in love with the should-be-dead-by-now imperial system (which is mostly the USA and PommieLand)) I'll explain something basic first a meter is a standard measurement, smaller units are millimeters and converting them is done by thousand. I know this is shocking to people who deal in inches because they'll never have heard of a thousandth of an inch being called a milliInch. (not to mention multiplying by 10 seems difficult for lovers of Imperial)

So how strong is a gauss?

Thats a good place to start, so from a quick google we find this:

A refrigerator magnet is 100 gauss, a strong refrigerator magnet. The typical strength of the Earth's magnetic field at its surface is around a half a gauss. So those are everyday units of magnetic fields.

So basically from this and the above table you could reasonably expect that if you sat a fridge magnet on top of your watch which was not marked with the U symbol shown above then it would be likely to be effected by that magnet.

If however yours was type 1 then as they say "A magnetic resistant watch almost always maintains its performance when placed at 5 cm from magnetic field generating devices of everyday life." This should leave you to be comfortable that unless you've sat a fridge magnet on top of your watch then there should be no effect and you can look elsewhere for reasons why your watch is not running on time. My first advice would be that you look at the actual specs for the movement, which are often a few minutes per day. If its an automatic perhaps you should just wear it, as it was designed to be worn.

But what about my phone?

yes, indeed phones can give you a magnetic field, this is usually measured in milligauss. Indeed if you dig around you'll find (on a now gone site, but you can find it on the wayback machine) that (in 2003) a common phone produced about 20 milligauss. For the maths challenged thats pretty small. 100 gauss is 100,000 milligauss and so 20 milligauss is literally nothing for a watch.

So basically you can stop worrying that your phone on the dresser beside your watch has magnetised your phone, and pretty much unless you are a technician working on CAT scanners you can rest easy (they'll probably already be resting easy because they'll know they shouldn't wear a watch) and give up that plan to buy a degaussing tool from eBay (which will probably result in your magnetising your watch anyway because you don't know how to use it).

Leave this one to the watch sub cult of King Wang