Landeron test watches? Maybe. Here we have a bit of a mystery. This box of 12 Landeron 4750 based watches turned up on a well known auction site recently. The watches are all identical, chrome plated cases, unbranded dials and their cases have been drilled in two places to allow electrical wires to enter/exit the case.

A red wire enters the watch via a hole in the battery hatch and connects to the -ve side of a dummy battery (see photos). The yellow wire enters through a hole in the case between one set of lugs and attaches to the contact wires — not the +ve side of the movement. So these two wires alone were not used to power the watches via an external battery; it seems likely that the red wire (-ve) and the case body (+ve) were used to power the watches while the yellow wire was used to measure something.

After speaking with my colleague David Read, it seems the colour yellow is often used in electronics to indicate output from something and David kindly carried out the following experiment.

A storage ‘scope is connected to the yellow wire and shows that pulses of 5Hz are emitted. This is to be expected because the frequency of an 18000 bph balance is 2.5 Hz. However, because it is impulsed on each vibration, the pulse frequency is 5Hz as displayed by the ‘scope. The pulse width is about 10 ms and can itself can be examined for quality of the contact surface by altering the time/division chosen for the display. A poor contact will be revealed by lots of fuzzy lines rather than clean edges. A long term test would reveal how long it took an initially clean contact to become poor. The purpose of the diode across the coil is to provide a path for the voltage generated by the collapsing magnetic field on switch off. If not present the potential involved will find a path by sparking which will corrode the contacts. David’s set up is shown here.

So what’s the purpose of this batch of 12 watches? David Read’s thoughts:

With the case backs in place and dummy cells made up to take in the negative supply , my view is that they can only have been modified in order to carry out longish term evaluation for some purpose using the same method as described above. I don’t mean prototype evaluation; that would all have been done by ESA in Switzerland before release. Ebauches S.A. made the 4750 available to their customers (Swiss watchmakers) via their Landeron division in April 1960. Time quickly passes and it wasn’t until December of that year that an announcement appeared in the Watchmaker and Jeweller under the title of The First Swiss Electric Watch. This covered Avia’s release and it was sufficiently novel to be in an 18ct gold case. It would have been well into 1961 before significant sales built up. I don’t know what happened with respect to distribution in the USA but perhaps some batches were sent with unbranded dials for independent evaluation by Wittnauer so that they would be confident in whatever claims they would make for their release on a market that had seen electric wristwatches for rather a long time. I agree that the postmark on the box seems late but it is often quite a while (even years) before very small initial sales (say in Switzerland) would build up to full production and large worldwide sales. Also, I don’t think that that particular posting is an indication of the date that the watches were received in the USA. It seem quite likely that after a long term test, the wires were trimmed off the watches and they were posted within the USA. Perhaps they were being returned from a standards lab. to the marketing department of Wittnaeur together with a report.