Demagnetizing Watch Movement

I ship hundreds of watches per year all over the world, and have had no problems with magnetism that I can recall. Lots of things thrown around in this thread so far, so I'll address a few:

1 - Magnetism comes from magnetic fields, and these can be permanent magnets or electrically produced. In my experience, iPad covers are one of the most common culprits these days - the covers are full of fairly strong permanent magnets. Keep in mind the field strength goes up dramatically as distance closes - not a linear relationship.

2 - Magnetism can affect any ferrous part in a watch, not just the balance spring. Although many people believe that only huge gains in rate will result from magnetism, that isn't always the case. I have seen coils so stuck together that the balance barely turns at all, and the rates were very slow - even some where it stopped the watch, but these are exceptional cases. Note that other parts of a watch being magnetized can cause other problems not related to timekeeping.

3 - As noted, using any old compass will not tell you much - I personally don't bother which such things and use the timing machine...

4 - Expecting every vintage watch that has been serviced to run +/- 10 seconds per day is completely unrealistic. Timekeeping performance will depend heavily on the condition of the movement, and skills of the watchmaker. If parts are worn out, replacements are not available, and the watchmaker doesn't make new parts (either because of the lack of skills, or lack of money on the part of the customer) then accuracy will suffer. In this particular case, the Cal. 353 and all the bumpers do have a lot of parts that are no longer available, and quite frankly someone selling a watch for profit is not likely going to go to the expense to have parts made for a watch like this, or even go after donor watches for parts as it would cut into their profit.

As a reference Omega's specs for the 353 are that the average daily rate is between -1 and +16 seconds. Positional variation can be as much as 40 seconds at full wind, and 50 seconds 24 hours after full wind, measured over just 3 positions. Not saying that these movements can't run to near chronometer specs because I've done it, but to expect that from every serviced watch is just not realistic without spending serious money typically.

And of course the claims that it was "freshly serviced" are pretty meaningless unless that is backed up by documentation from a known good service provider.

If the watch is running consistently slow, then most likely regulation can improve it.

Cheers, Al

"As the name suggests, watches will usually get magnetized around big/strong magnets. Computers have magnets in their speakers for example. Many have had their watches magnetized because of the magnets in their tablet cases."

Computers have VERY strong magnets in their hard drives. So strong, you don't want to put one in each front pocket 😲

My recommendation for those collecting vintage watches and wanting to wear them consistently is to emigrate to Canada and move next door to Al. Be sure to give him friendly wave and a big howdy neighbor each morning. 👍

Me too since I am not in Toronto...

Well, just so happens a magnetized watch came in for service, in this case a Sinn U1 using an ETA 2824-2 movement. Primary complaint from the owner was a very fast rate, so I fully wound it and put it on the timing machine yesterday:



Two numbers to pay attention to here - the first in the number 173, and this is the balance amplitude, so the number of degrees the balance swings (average of both directions). It's very low.

The second is the daily rate, and here it's quite fast at +158 seconds per day, so dial up this watch will gain around 2.5 minutes per day.

I quickly put it on the demagnetizer, pressed the button twice, and put it back on the timing machine:



Now the balance amplitude is up to 250 degrees, and the daily rate is just +4.3 seconds per day. Now the low amplitude does indicate there is still a need to service this watch, but the daily rate came right to a pretty good number with about 5 seconds of work...

Have since disassembled the watch and oils were drying out, parts are starting to wear, so this still was in need of servicing, but this illustrates the most common result of a magnetized watch on the timing. I have done this exact same thing with watches that were only running 30 or 45 seconds fast per day, and had good amplitude, and demagnetizing brought them right back to where they should be.

Cheers, Al