[evlatests] Consequence of IAT clock error

[Rick Perley]

    The clock error which was found and corrected yesterday appears to 
have resulted in the following:

    a) A loss of ~ 25% in sensitivity on EVLA to VLA baselines
    b) Closure errors of up to 100% on EVLA to EVLA baselines. 

    Hence, data taken from the time the clock error began (probably 
Thursday during maintenance time -- but this has yet to be established) 
until its correction (during software time yesterday) are severely 
compromised.  Users should flag their EVLA to EVLA baselines.  EVLA to 
VLA baselines do not show any closure problems, but are reduced in 
sensitivity.  VLA to VLA baselines are unaffected. 

    I believe that the new 'L350 1PPS' device, soon to be implemented, 
should eliminate this kind of mis-timing.  Testers should note that by 
far the easiest way to detect this problem is to set the closure report 
level (within CALIB) at 50% or so.  (I had discontinued looking at 
closure myself because of the large number of moderate level (10 -- 20%) 
errors from the bandpass mismatch problem was cluttering up the screens).