JWST dithers and their precision are covered in this article.

See also: JWST Dithering Overview

Dithers (small re-pointings) less than 60 mas are executed with the fine steering mirror while maintaining closed-loop guiding on the guide star.

Dithers between 60 mas and 25" are executed by dropping closed-loop guiding, slewing, and re-entering guiding at the track mode stage. 

Dithers larger than 25" are executed by dropping closed-loop guiding, slewing, and then restarting guiding at the guide star acquisition stage.

The accuracy for all 3 types of dither are usually 2–4 mas rms (1-σ per axis) on the sky. For larger dithers the offset accuracy may be a few mas larger due to residuals in the astrometric calibration of a particular science instrument.