Table of Measurements of V-null

The procedure for measuring "V_null_encoder" is given in my posting to the 
analysis logbook in August 2006.  This is a quick-and-dirty way to 
meaasure the HWP flag.  John gives a fuller discussion of this and other 
ways to do grid tests under "8. documentation" on the main "teamsite" 
page.
_________________________________________________________________________________________________
DATE          PAGE # OF LOGBOOK       CONDITIONS        V-null_encoder	       V-null_enc (fit)


July '06      analysis logbook        -                 93 +/- 2	       94.5 +/- 0.8
              (August '06 post)

Dec. '06                                                                       53 (from JEV posting)
 
Feb 9, '07    log #1 page 185         no nylon          95 +/- 2	       95.5 +/- 0.3
                                      wires vertical

Feb 11, '07   log #1 page 187         nylon             95 +/- 5

Apr 30, '07   log #2 page 12          2.5 deg CW frm    95 +/- 2	       95.0 +/- 0.1
       
                                      vertical          (H/V ambiguity?)

June 10, '07  log #2 page 23          wires vertical    53 +/- 3	       59.4 +/- 0.5
                                      within 1 degree

Aug. 8, '07   log #2 page 29          wires vertical    96 +/- 2
                                      within 1 degree
                                      no nylon

Aug. 12, '07  log #2 page 31          same as previous  97 +/- 2	       96.5 +/- 1.5

Dec. '07                                                                       52-53 (JEV E-mail)

_________________________________________________________________________________________________


(fit) values are from a sinusoidal fit to an entire 90 degree HWP cycle with data taken every 10 degrees.

Note that the value of the flag "HWP" can be found from the formula in
my Aug. 2006 posting to the analysis logbook:

  HWP = 2 * V_null_rel = 2 * (V_null_encoder - "first_angle")

The value of "first-angle" was 50 for all of the above runs, except for
the Dec. 2006 run, where it was 200 (same as 20).

Thus, the values of HWP range from 86 to 94 for all of the above 350 
micron runs.  It makes sense that HWP should be constant since we 
installed the 350 micron hwp approximately the same way for every run 
starting with the July 2006 run, and since the encoder swap done in April 
2007 resulted in a 179 degree change in the meaning of the angles, which 
should not affect the HWP flag much.

we get HWP = 66 for the 450 micron run in Dec. 2006

we get HWP = 6 OR HWP = 19 for the 450 micron run in June 2007