The Seiko caliber NE20 is a movement produced by Seiko Watch Corp. in their Seiko Instruments/Time Module branch. Tech docs for this caliber were found dated as far back as May 2010, so this movement has been around for at least that long.
Some of the topics covered in this caliber listing:
Caliber NE20 VS NE20A, NE20B, NE20C:
The letter at the end of NE20* indicates an evolution of the NE20 (NE20A, NE20B, NE20C, etc). The official tech sheets for the caliber NE20C were updated on December 14, 2021. The differences between each iteration is unconfirmed. If you have insight into this, please comment below.
Seiko claims that the accuracy of caliber NE20 is between -15/+25 seconds per day. This rating is based on normal daily wear on the wrist in normal operating temperatures.Seiko tests the accuracy in 3 positions: dial up, crown down (9:00 up), and crown left (6:00 up). When testing your watch for timekeeping, make sure it is fully wound (see below).
The caliber NE20 holds a power reserve of greater than 45 hours. To fully wind the mainspring, turn the crown a minimum of 55 times. There is a power reserve indicator located at 9:30 on the dial.
Crown Position Functions:
0 (against the case): Clockwise = Manual Winding / Counterclockwise = Nothing
1 (pulled out one click): Clockwise = Day setting / Counterclockwise = Date setting
2 (pulled out two clicks): Time setting clockwise and counterclockwise
To remove the stem, make sure the crown is in position 0 or normal position (not date or time setting position). There is a lever with a small indentation for your tool. Gently press down while pulling the stem out. See official instructions below for more guidance:
At the time of this post, prices for replacement NE20 movements were found online for $285.00 to 388.95 USD.