Mesu 200 and Meridian Flip


I was convinced that I saw a post yesterday from a chap who was finding that his Mesu 200 would no longer perform a meridian flip. I cannot find his post now. I am having the same issue. The Mesu used to flip quite happily in SGP. A link to the logfile is attached:

SGP LogFile

Meridian Flip using slew commands?

What was your mount showing for time remaining versus your mounts ability to flip? As I’ve learned, SGP just makes the calls, it’s unlikely that SGP is the source of the problem other than if you put in the wrong time before/after meridian.

Based on your logs, SGP commanded the flip and your mount driver failed to perform it.

Next step when I’m troubleshooting meridian flips, I’d turn on very detailed logging for your mount driver in ASCOM and see what happens at the time SGP calls the meridian flip. You can do this during the day too. It should be pretty apparent if your mount is throwing an error.

Hope that helps,


@gnomus Did the Mesu 200 driver change recently?

For pier flips, SGPro supports two different kinds of mounts… those that allow us to send a command to flip and those that don’t (then we use normal slew commands in lieu of this). By all accounts, your mount is reporting to be the former. It is telling us that it will allow us to set the pier side and a flip should ensue. Here you can see us set the pier side to east, but nothing happens at the mount:

[15/02/2016 17:59:27] [DEBUG] [Pier Flip Thread] Meridian Flip: Sending Telescope command to execute meridian flip
[15/02/2016 17:59:27] [DEBUG] [Telescope Thread] ASCOM Telescope: Pier side is West
[15/02/2016 17:59:27] [DEBUG] [Telescope Thread] ASCOM Telescope: attempting pier flip using sideOfPier
[15/02/2016 17:59:27] [DEBUG] [Telescope Thread] Setting Pier East
[15/02/2016 17:59:29] [DEBUG] [Telescope Thread] ASCOM Telescope: Pier side is West
[15/02/2016 17:59:30] [DEBUG] [Pier Flip Thread] Meridian Flip: Telescope command to meridian flip has completed
[15/02/2016 17:59:30] [DEBUG] [Pier Flip Thread] Meridian Flip: Telescope failed to perform meridian flip


I have taken this up with the Sitech chap. If I get a resolution, I will post here.


This problem is now fixed. The original ‘Help’ file that came with Sitech.exe had some errors in it and this made things somewhat confusing.

The issue is the new dialogues in Sitech for Over and Under Pole settings. This sets a ‘window’ (shown as Green lines on Sitech’s SkyView program) within which the mount will happily track. In addition, there is the option to set a number of degrees that the mount will track past those Over and Under Pole settings before the mount will stop tracking.

I had SGP set to flip 6 minutes after the meridian. In Sitech, I had Over/Under Pole settings of +/- 1 degree (roughly 4 minutes, I believe) with the ability to track past these limits a further 3 degrees.

This meant that when SGP issued the meridian flip request, the mount was always pointing somewhere after the Over/Under Pole limits (but before the ‘Track Past’ setting) – that is between the Green and Blue lines on SkyView (it is helpful to have a look at SkyView when you are setting this up). On the current version of Sitech, the mount will not perform a flip if it is beyond the Over/Under Pole limits. So current users need to set things up so that the flip will always happen within those limits.

Dan is rewriting the program so that the mount will perform a flip if it is after the Under/Over Pole but before the Track Past. I have tested an early version of this and it is working. He hopes to release this version soon.

In the interim, folks will need to ensure that their meridian flip command is issued within the Over/Under Pole limits.

Only a few days ago I wouldn’t have had a clue what any of the above meant, by the way, so I apologise if it is not very clear. As I said earlier, the ‘Help’ file contains an error that will have people putting in the incorrect settings. So I will give an example that works:

I set SGP so that it will issue a meridian flip 0 minutes after passing the meridian. Do not ask SGP to Wait for Centering. I then go into the SItech config file and set the following in Mount Parameters:


10:00:00 —Meridian Limit West (Degs)— **-**170:00:00
**-**10:00:00 —Meridian Limit East (Degs)— 170:00:00
03:00:00 Track Past Meridian Overlap

You can adjust these numbers to suit yourself, but pay particular attention to the plus/minus signs – it is these that are incorrect in the current help file. You will have to check that a +/- 10 degree overlap will not result in you suffering a pier strike (my camera gets pretty close but just clears at these settings).

What this does is tell SGP to issue a meridian flip instruction as soon as an opportunity arises after the meridian. Sitech will continue to track past the meridian for 10 degrees (roughly 40 minutes) and it will then flip (in SGP the ‘time to meridian’ number becomes negative and keeps counting). In the current version it will not flip if it gets further than 10 degrees past the meridian so (for me) the ‘Track Past’ setting has no function. As I said, Dan is planning to issue a version that will allow for meridian flip between the Meridian Limit and the Track Past.

I hope this is clear. I am happy to answer questions if people have them, but I am no expert in these matters (as is probably obvious).


Hi I wonder if you could help me please? I have a MESU 200 and a Celestron C11 mounted on it in a fixed observatory on a pier. Also Sitech II. I don’t know how to set the limits so that my kit doesn’t crash the pier… I cannot understand the documentation and have been in touch with Dan, but still not able to work this out. I tried to get a definition of over pole and under pole but don’t get that either.

Is there a process you followed to get the required numbers for the east and west limits? Could you share it?

Many thanks,


I am in Germany at the moment and have limited internet access. I wrote a lengthy post on the SGP forum so if you can find that it will tell you as much as I know. I won’t be back home for another couple of weeks so won’t be much additional help until then. If you can’t find the SGP post let me know and I will find it for you - I may not be able to do that before Wednesday when I change hotel.


thanks Gnomus - the only piece I can find is the one in this thread. Thanks for your help.



OK Paul. I have Internet at the moment, but who knows how long that will last. The over and under pole settings are confusing. One set of numbers sets the absolute hard limit at which the Mesu will simply stop tracking. The other set, as far as I can tell, exists so that if there is an object that is just on the other side of the Meridian, you can get the mount to slew to it without flipping. (It may be useful to do this for a quick observation, or to pick up a couple of quick subs).

If you are concerned about the possibility of a crash, then set the hard limit to a relatively low number. Set the others to be within this. If you go into SkyView (part of Sitech) you get a graphical representation of the limits you set. Pay particular attention to the positive and negative numbers - it was this that was wrong in the original help file. You could follow the pattern I have outlined above, but just reduce the numbers to suit your situation.

If it is any consolation, I ‘think’ the mount will stop trying to track if it comes up againts a mechanical obstruction. Someone who knows a great deal about these mounts told me this, but I cannot say for certain if it is true or not.



So to be clear, if you set the Meridian Limit West to ‘05.00.00’ and ‘-175.00.00’; then the East settings to ‘-05.00.00’ and ‘175.00.00’, then the mount will happily track 5 degrees either side of the Meridian before stopping. You need both sets of numbers (I believe) to take account of situations when the mount is pointing Northwards and Southwards.

If you set the Track Past to (say) 1 degree (as I say I’m travelling so cant check, but this may actually be minutes of time not degrees) the mount will actually go a bit beyond these limits before stopping. This is handy because it would eba nnoying to hit the limits 19 minutes in to a 20 minute sub. You can change these numbers on the fly.

You could use the Mesu handset to slew to a position that is safe and the read off the information from the Sitech pop up window. This would give you an idea.


thanks Steve - I’ll see if I can make sense of this when I get to the mount. One basic question is - in your text above, where does 175 come from? Why would you enter that as a limit? i.e. what informs the values to be used? Is there some datum?

thanks again,


Well … South is 180 degrees. So +5 and -175 are 5 degrees either side of that. You need to choose how far past the meridian you can safely go. I can get to +/- 10 without any issue.


Or, if this makes it easier, think of two lines - one running from 05 to -175 (or 185 if you prefer to think only in positive numbers) on the compass rose; and another running from -5 (or 355) and 175. The area in between represents your meridian limits. A quick look on Skyview makes it very clear.