S. Epson Caliber YM04A

Manufacturer	S. Epson (Seiko owned)
Caliber Number	YM04A
Movement Type	Quartz, battery-powered
Movement Class	Chronograph, big-date
Lignes	12”’
Diameter	27mm
Height	4.93mm
Jewel Count	0 (no jewels)
Frequency	32,768 Hz
Accuracy Rating	+/- 20 seconds/month
Battery Cell	SR927SW (395/399)
Battery Life	5 years
Regulator?	None
Hand Count	6
Hand Sizes	1.10mm / .65mm / .21mm / .21mm x 3
Functions	Central hours; central minutes; central chronograph hand; small seconds hand at 9:00; 60 minutes chronograph counter at 6:00; 24 hour indicator at 3:00, big double digit date at 12:00
Hacking Seconds?	Yes
Country of Manufacture	Made in Japan
Known Models	Invicta Aviator (model 1233) (Add your watch to the comments below…)

Seiko Epson caliber YM04A is a quartz chronograph watch movement with a big date and 24 hour indicator.

Examples of watches with this movements:

This example of cal. YM04A was found in an Invicta Aviator watch. Notice the extra long chronograph pusher stems needed to accommodate the 27mm movement in a 48mm diameter case.

Additional Resources:

• List of Seiko watch movements
• More S. Epson watch movements