latest alignment object.  Because there are several parameters in the model, it won' t 
converge on nominal values until you have performed at least 4 or 5 alignments on one 
side of the meridian.  As mentioned earlier, you will get the best results if you pick 
alignment objects with substantially different hour angles.   An additional source of 
inaccuracy   gear play   is calculated with the first alignment on the opposite side of the 
meridian. 
3.5.2  System Startup Modes 
Because Gemini stores the modeling parameters in non volatile memory, it may be 
powered off at any time without losing its pointing model. In fact, the model can continue 
to be refined from observing session to observing session by adding more alignment 
points.  However, the modeling parameters are only valid if the telescope and mount have 
not been moved between observing sessions.  Whenever you turn the Gemini unit on, you 
need to tell it whether anything has been moved since it was turned off.  This allows 
Gemini to decide how much of the model is still valid.  There are 3 startup modes that tell 
Gemini what has been moved: 
  
Cold Start
  
Warm Start
  
Warm Restart
When the Gemini is powered up for the first time or after a CMOS reset, "Cold Start" is 
the only menu choice since there was no valid model in memory.  Once a model has been 
established, subsequent power ups will add "Warm Start" and "Warm Restart" to the 
startup menu. 
"Cold Start" is the "start from scratch" startup choice because it deletes all previously 
established model parameters derived from previous alignments.  It is the startup mode 
that must be used anytime the mount has been moved from its previous polar aligned 
position. 
Upon selecting "Cold Start,   Gemini allows you to change the UTC Date/Time, 
Longitude, and Latitude (level 3 version 1.01 and higher).  You should enter these 
parameters at this point unless they are still valid from a previous observation, or were 
provided by a GPS receiver that was connected to the Gemini when it was powered on.  
For Gemini version previous to level 3 version 1.01, you should use the   Setup   menu to 
change these parameters if necessary. 
Assuming Gemini was powered on with the telescope in Startup Position, the user can 
easily find a first alignment star by navigating to the "Databases" menu, selecting a star 
from the Bright Star Catalog, performing a GoTo operation, centering the star in the 
telescope 
s field of view, and then selecting "Synchronize."  This constitutes the initial 
star alignment in the process of building a pointing model.  Subsequent star alignments 
can then be performed one at a time by slewing (via GoTo) to other Bright Stars, 
centering, and executing "Additional Align." 
Gemini Users Manual 
3  
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