Yes, we all know it is the 1st who is remembered and matters (*klikk) -- and this is true for the most relevant category and the defining complication in watchmaking: miniaturization (*klikk). The drive to miniaturization in electronic watches is on since 1930s, when quartz was used first, but it is in full speed since 1969 and reached its first peak (local max) in 1978 when Citizen presented the cal790 -- expensive, rare and very important -- with less than 1 (!sic one) millimeter thickness (0.98mm) of the movement. A first and important. The whole watch was cased in classic way and measured 4mm in total.

And we can show you a rare, working and well preserved 18K-whitegold example of this watch, made in January 1979 -- calling it a #horologicalMilestone is not wrong. We know that the "Thin Watch War" didnt end here: it was ETA with the cal999.001 Delirium Tres Mince and the innovation to use the caseback as main-plate to further (and finally) reached a total thickness of less than 2mm -- movement + hands + crystal + case, all inclusive.

NB: Miniaturization is the defining complication of watchmaking? Yes, because without this complication your minute-repeater or your perpetual calendar comes in size of a car and is a clock.