Worse after the meridian flip

Compare the last sub before the flip with the first one after it. The change is a step, with no slow decline before it.

1. 01

   Cable drag

   A cable with slack going east and none going west snags at every flip until it is rerouted.

   FixAfter any change to the train or the cabling, dry-run a meridian flip in daylight and watch every cable through it.

   Session Checklist
2. 02

   Balance on the wrong side

   A rig balanced slightly east-heavy before the flip is west-heavy after it, so the drive and the guider see a different load.

   FixRecheck balance after the flip, declination first, then right ascension.

   Session Checklist
3. 03

   Pier or tripod collision

   The train is longest past the meridian just before the flip, pointing low. That is where a camera meets a pier or a tripod leg.

   FixCheck that the camera, filter wheel and any rotator clear the pier or tripod legs at the hour angle the flip happens, with the night's longest train.

   Session Checklist

• A change in the seeing

  Seeing worsens gradually over the night. A flip problem is a step at the flip.

One frame cannot show this. It takes the subs in time order, with the flip time marked.

Subs after the flip as good as the ones before it, and a guide graph that looks the same on both sides.

No outside source is cited here. The signature, the causes and their order are the atlas’s own, from imaging experience. The order is a judgment of likelihood; no measured frequency is behind it.