Seiko Cal. 4R71A (commonly called just Cal. 4R71) is a partially-skeletonized and open heart mainstream automatic movement. It is also offered by Time Module Inc. (TMI) as Cal. NH70A and NH71A (gold plated) for use by other watch makers. It is closely related to the date-only Cal. 4R35 and 4R38.

First appearing in late 2017 for the 2018 BaselWorld releases, Cal. 4R71 has only been used in two limited-edition Seiko Premier watches.

Hand winding is accomplished with the crown in first position, rotating clockwise.

	Traditional Mainspring Hacking/Hand-Winding	Spron 510 Mainspring
Standard	4R38A NH38A 4R71A (skeleton) NH70A (skeleton) NH71A (skeleton, gilt)
Date	4R35A 4R35B NH35A	4R15A 4R15B NH15A
Day and Date	4R36A NH36A	4R16A 4R16B NH16A
Date, 24 Hour Subdial	4R37A NH37A
24 Hour Subdial	4R39A NH39A
Date by Pointer Power Reserve	4R57A