From what I read here in the forum, but also in the other discussion groups, the GO Senator Perpetual is an extremely popular perpetual calendar, and chosen by many watch lovers. To a major part, this success is certainly based on its highly legible dial layout. However, I think it is safe to state, that another important reason for its popularity is the fact that it is offered in stainless steel as well, and therefore is among the least expensive perpetual calendars on the market.
The more astonishing it is for me, that the Senator's little brother, the Union perpetual, apparently has not been able to develop a similar desirability. The Union perpetual uses the very same perpetual calendar mechanism as the GO Senator, with the only difference that weekday and month are not displayed in windows, but - more conventionally - with small hands on subdials at 10 and 2. From a technical point of view, this construction even offers a slight advantage: due to the smaller mass that has to be moved (small hand vs. disk), bumps and shocks are less likely to cause maladjustments. Another, more important difference, is the use of the Union cal. 26 as base movement. This movement, while technically marvelous, cannot compete with the GO cal. 39's hand-applied finish, of course; but it is still a very beautifully made, solid and reliable in-house movement, produced on the very same machinery and assembled by the same watchmakers as the GO movements. And it should be mentioned, that the Union perpetual is substantially cheaper than its big brother with the Glash?tte Original label.
There are three variants of the Union perpetual:









