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Is it over shooting on RA - causing an oscillation?
I ponder are your min pixel movement before a guide command is issued to sensitive. It defaults to 0.20 of a pixel (and can see down to 0.01 Craig told me). However I generally set mine to 0.8 - 1.2 depending on seeing, focal length of guide scope and pixel size of guide camera. The key factor is are your arc/seconds per pixel on your guide scope too sensitive for your viewing conditions. If a pixel is only seeing 0.5 arc seconds and seeing isn't really better than 2-3 well you are going to be over correcting everywhere - and your chart looked like that to me.
I suggest:
Turn backlash to 0 on RA and DEC - definitely let PHD manage this.
Try and adjust pulse length so it takes 15 - 30 pulses to move the star sufficiently to calibrate.
I set RA aggressiveness to about 85% and Hysteresis to about 10%. Purists suggest more aggressiveness (95% - 100%) and less hysteresis (5% - 0%) when calibrating and about my levels when guiding.
Experiment with minimum pixel movement before guide pulse is issued from 0.2 up in 0.1 increments to see where your sweet spot is (seeing based). Definitely use the PHD chart function and look at the Osc(illation) index - you want that as small as can be.
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