The short answer
When we say a mechanical watch has been serviced, we don't mean that it has simply been checked, regulated or had a little oil added.
A proper mechanical service involves dismantling the movement, cleaning the components, inspecting them for wear or damage, reassembling and lubricating the movement, and then adjusting and testing the watch.
It's much closer to rebuilding a small machine than giving it a quick tune-up.
From the bench
A mechanical watch movement contains dozens, sometimes hundreds, of components working together. Many of the surfaces involved are tiny, and the quantities of lubricant used are smaller still.
Over time those lubricants deteriorate, migrate or dry. Dirt and microscopic particles can accumulate, while pivots, jewels, springs and other components can develop wear.
Simply adding fresh oil doesn't remove what is already there.
During a service the movement is dismantled so its components can be properly cleaned and inspected. Worn or damaged parts can then be identified rather than hidden by adjustment.
Once cleaned, the movement is rebuilt and the correct lubricants are applied where required. The watch can then be adjusted and tested.
With a vintage watch there is another consideration: preservation.
The objective isn't to make a fifty-year-old watch mechanically or cosmetically new. Original components should be retained wherever they remain serviceable, and replacement should be considered when a component's condition affects the proper operation or reliability of the watch.
That judgement is an important part of servicing vintage watches.
What we recommend
When buying a vintage mechanical watch described as serviced, don't be afraid to ask what the seller means by the word.
Inspected, tested, regulated and serviced are not interchangeable terms.
A watch can produce an attractive reading on a timegrapher without having been serviced, just as a freshly serviced vintage movement doesn't suddenly become a brand-new movement.
What matters is understanding what work has actually been carried out and having realistic expectations of a mechanical watch that may already have been working for half a century.
At Past2Present, when we describe a mechanical watch as serviced, we mean that the movement has been through the servicing process at the watchmaker's bench.
A timegrapher can tell us how a watch is running. A service lets us find out why.