The Gemini PEC can store 2 separate sets of correction data.  One set, called the   current 

data set   is used to actually correct for periodic error.  It is initially stored when the first 

PEC training is completed.   The other set, called the   backup data set   is used for 

backing up and combining PEC data.  These data sets will be described in more detail in 

the following sections. 

4.3.2.1  Train PEC 

Until an initial (current) data set has been recorded, no PEC data is available to the 

Gemini software.  Also, a CMOS reset or the execution of   Restore Defaults   or   Clear 

Data   clears all PEC data and, in all these cases, only the first PEC menu item   Train 

PEC 

is visible and available for use.  

Once you select   Train PEC,   you start a training session, where your task is to keep an 

object (preferably a star near the meridian) centered in the crosshair of an eyepiece or at a 

given CCD pixel location.  You have about 18 seconds to center the object used for the 

first training, while a countdown (  Training PEC  xx  ) is displayed. A short beep marks 

the start of a training session, and another beep marks the end of training after one worm 

period.  The length of a training session will vary according to the period of the worm 

rotation on your mount.  This is 4 minutes on a G 11, HGM 200 and MI 250, 5.33 

minutes on an HGM Titan, and 8 minutes on a GM 8 and CI 700.  You can interrupt the 

training session by depressing the MENU button on the Hand Controller.   

The countdown time for subsequent training runs will vary, since training is always 

started at the same point on the worm.  Thus, you may need to wait up to 8 minutes (on a 

GM 8 or CI 700 mount) to do additional training runs.  You may do as many training 

runs as you desire. 

After each training run, the PEC data just entered is stored in the current data set, and is 

immediately available for use.   Any previous data is moved into the backup data set 

where it can be manipulated by several of the other PEC commands. 

4.3.2.2  Clear Data 

Selecting this menu item clears both PEC data sets and disables PEC correction.  This is 

useful if the PEC data becomes invalid because you have removed the RA servomotor.  

This command also reduces the PEC menu to just   Train PEC.   

4.3.2.3  PEC On/Off 

Selecting this menu item toggles the PEC function on and off.  If PEC is currently off, 

this menu item will turn it on (changing the menu item to   PEC Off  ), and vice versa.  

Gemini' s PEC can be switched on or off without affecting any of the stored data.  PEC is 

turned off when the Gemini is first powered up, so you need to select this menu item each 

time you start the Gemini if you want PEC to be active. 

Gemini Users Manual 

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