[Bteam] injector relative orbit and zero pos

[Jay Benesch]

Assertions

1. with two high current halls the orbit is the weighted average of the 
beam centroids

2. Qweak charge asymmetry is related, for reasons unknown, to the amount 
of beam scraped off on A2

3. When Ops does a save with zero position it saves the relative orbit 
for all BPMs

4. Injector autosteer relies on the relative orbit


Conjecture

0R04 trips may be related to the relative orbits of the A and C beams. 
http://opweb.acc.jlab.org/CSUEApps/elog02/elog_item.php?elog_id=1579572


Suggestions

"Zero position" option in SAVER should be modified from yes/no choice to 
three choices:

a. zero position for injector "[0123]I", 0L, 0R
b. zero position for everything else
c. no ZP

Ops could choose any one or the a/b pair.

For restore, there could be a few more templates at the end under a BPM 
restore "menu": injector, machine, hall A, hall B, hall C.  Or people 
could simply be required to continue to grep the needed BPMs when 
restoring a relative orbit.

Jay