REPEATABILITY TESTS FOR ZENITH DISTANCE 


These numbers represent the deviation along the drive circle (appx 50 inches 
in radius) measured with a dial indicator after the telescope is driven away from 
a position by a given distance (in encoder counts) at a given rate (in encoder 
counts/sec) and then driven back.  The scale is roughly 4 arcsec per 0.001 inches.
Rrrors are of the order of 0.0005 inches (+/-2 arcsec).  We used the number of 
steps under "Distance"; the corresponding angles are very approximate.
The oscillation test drives the axis sinusoidally and looks for the amplitude 
of the changes in position.

_____________________________________________________________

Rate -->            10 cps          200 cps       70,000 cps
_____________________________________________________________
              |
Distance      |
              |
6,000 steps   |    0.0002in         0.0000in          N/A
(10 arcmin)   |                     0.0005          
              |
36,000 steps  |      N/A           -0.0003            N/A
(1 deg)       |                     0.0004                      
              |
360,000 steps |      N/A              N/A           0.0009
(10 deg)      |                                     0.0009  
              |                                     0.0011  
              |
725,000 steps |      N/A              N/A           0.0022
(20 deg)      |                                     0.0028  
              |                                     0.0015  
              |                                     0.0018  
              |
2,225,000 stps|      N/A              N/A          -0.0043 
(60 deg=appx  |                                    -0.0048  
 full range)  |
______________|______________________________________________
              |
              |
Oscillation   |   Range = 0.0012 in 
test          |
______________|______________________________________________