[Shiraz (Ray)]

that's a difficult one Lee.

drift errors like this must be annoying and very disappointing for an expensive mount. However, Dec Backlash and RA gear jitter are way bigger menaces than a slowly varying RA rate drift like this if you are guiding - if you have little backlash and jitter and the RA drift guides out, then you will get results as good as any mount.

Looking at your graph, maybe the makers have a point - if you guide, it should be fine, since the error slew rate is not very high (almost always less than an arcsec every 3-4 seconds) and the jitter looks small. Although the extent of the drift is quite large, it varies slowly and smoothly - way better than an EQ6 for example. It isn't perfect in one respect, but if it does OK otherwise and that one problem can be managed, then you have a good mount. The makers suggest that it a very capable guided mount - they don't make any claim for unguided performance.

So the question is, does it have negligible dec backlash and can it routinely produce tight round stars with guiding? If yes, then you have a good mount - forget that it isn't quite perfect - it is good enough for the job and will possibly do better than a gear driven one due to the smoothness of the belt drive. If no, then you may need to go through the hassle of trying to get the supplier to give you a refund.