The offsets sent to the telescope for jitter observations, both in imaging and spectroscopy, are stored into 8 keywords. This applies to AutoJitter, AutoJitterOffset, and GenericOffset templates.
Cumulative offsets are always relative to the first frame in the batch (TPL.EXPNO=1). Relative offsets are always relative to the previous frame (TPL.EXPNO-1) in the batch.
If the same guide star is used before and after an offset, the offsetting accuracy is about 0.1 arc seconds. All recipes looking for offset information take this into account and will use the header offset information as a first guess and will refine the offset through cross-correlation techniques.
In AutoJitter mode, the jitter offsets are generated using a Poisson distribution. SEQ.POISSON is an integer describing the Poisson homogeneity factor used for this distribution. See the eclipse web page (http://www.eso.org/eclipse) for more information about this factor.
The jitter recipe from eclipse always expects offsets to be given in pixels, not in arcseconds. If your headers do not mention the offsets in pixels, you must translate arcseconds to pixels yourself and feed the information back into the jitter command. The input offsets are then given by an ASCII file instead of being read from the FITS headers.