What does the plus label mean when buying a watch?

When buying a watch, the plus label means the unit of measurement that tells you a watch's accuracy. The label typically reads +/- X seconds per day or +/- X sec/day, with X being a number, such as 3 or 5. These measurements tell you how many seconds a watch gains or loses, and the smaller the number, the more accurate a watch is when properly stored, cared for and maintained. On 1stDibs, find a large collection of watches.