El Primero 3604 is a manufacture movement by Zenith.

Automatic column-wheel chronograph movement, able to measure and display the 1/10th of a second. Based upon the calibre Zenith 3600 from 2021 with power reserve of 60 hours and stop-second mechanism.

This variant features an open base plate and bridges that allow for a clearer view of the high-frequency 5Hz escapement with lubricant-free silicon escape wheel and pallet lever.

Used e.g. with the model Zenith Chronomaster Open (2022).