ETACHRON is the name of a type of watch regulator system.
Despite being used by many Seiko calibers and listed as Seiko ETACHRON on some sites, ETACHRON is not a Seiko product. The ETA in ETACHRON comes from… ETA SA of the Swatch Group watch conglomerate. This is a widely used system found on some of the industry’s most popular watch movements such as the ETA 2824-2, 7750, 2836-2, Seiko calibers and more.
Although ETA appears to have filed for trademark protection for the term “ETACHRON” (not EtaChron, ETA CHRON, or other variations you may see) as recently as 2014, this regulator has been used since the 1970s (1977?).
ETACHRON uses a rotatable regulator pin “block” attached to the balance spring (hairspring), which is fixed to an adjustable arm.
Some of the topics covered in this caliber listing:
Regulator Pin Block – Rate adjustment. Brass. Located on the the upper arm with a more narrow gap.
Stud Block – Beat error adjustment. Nickel plated. Located on the lower arm with a wider gap.
Movement pictured below is an ETA/Valjoux caliber 7751
Fine-Timing Device – Sometimes with a screw for making minor -/+ timing adjustments. You may read that each line is about 5 seconds of adjustment, but different movements display the lines differently. Generally, you can adjust the rate +/-15 to 20 seconds with this screw. Notice the example at the top of this page (Seiko caliber 6R20) does not have a screw.
How to Regulate ETACHRON?
Seiko has included an excellent guide to regulating the ETACHRON device in their caliber 4R36 (pictured at the top of this page) technical guide. See the pdf below.
Tools for Regulating:
You may see watchmakers or tinkerers make quick adjustments using tweezers, but it’s also good to know that Bergeon and other brands have tools specifically made for fine-tuning the ETACHRON system. The tools are made for adjusting the regulator pin and stud without potentially damaging the hairspring. Bergeon’s general number is 31081, but you may need a special version (31081-EX-7750) for adjusting 7750 base movements.
Below is an advertisement for such tools that were actually sold by ETA. It was found in a 2007 copy of Horological Times magazine. The same publication also named the ETACHRON regulator as “one of the easiest regulator pins to adjust”.
Video: Identifying the blocks and regulating
Video: Macro adjusting the ETACHRON regulator pin with a tool