PHD graph

[Glider]

When PHD is guiding what does the Osc-Index and RMS figure represent?

I get 0.31 and 0.11 respectively. Is this good or bad, is smaller better?

I'm thinking it's deviation in pixels, and RMS is simply the root mean square of the Osc-Index figure.

[blinky]

I read somewhere that 0.3 is the best you can get but TBH I just look for the line to be as flat as possible.

[SteveL]

OSC index shows the odds of the guiding changing direction at the next update, (i.e its the oscillation index). A value of 0.31 is pretty good, its a 31% chance that the guiding will switch direction at the next update. I never really spent much time working out what values I should be aiming for as it just worked from day #1 and I never needed to bang my head against it.

Unsure what the RMS values are, probably showing the RootMeanSquare value of the size of updates (i.e pixels)

[James]

Have a look at the two pictures in my post here. As you can see with the guiding being very erratic the RMS error is much larger (and is bad). There was nothing wrong with PhD i.e. it was guiding as well as it could hence the OSC index is OK but there were such large jumps in RA that the RMS is bad.

Worth noting that while a high RMS isn't good, if the error is generally spread around you'll end up with larger stars which may or may not be a problem. In my case with my mount the movement was dramatic and on just the RA axis so my images were showing elongated stars from the tracking jumping back an forth - which is bad whichever way you look at it.

James