[Aavso-photometry] Comp and Check star variations using AIP's ver 2.2.0 Extended format.

[John Ott]

I'm not quite sure what to make of large comp and check variations over 
a long time series using AIP's ver 2.2.0 Extended format.

When doing differential photometry, and prior to submitting an AIP4Win 
Extended report, as I suspect many folks do, I run my series through the 
differential report tool to look for an ideally flat comp minus check 
plot.  In one recent time series, the Differential report shows a C2-C1 
change of 0.103 mag over a sequence lasting two hours.  For the exact 
same sequence in the Extended report format I see the comp and check 
star values change as much as 1.51 mag.  It appears that the Extended 
report's comp and check output is based, at least in part, on what I've 
set the zero value point at in the multi-image photometry tool.  It is 
unclear to me what to make of such huge variations in comp and check 
values and what use they could be to the AAVSO.

Are these comp and check values something I should be paying attention 
to if doing differential (vs. All-sky) photometry?

Where the AIP 2.2.0 Extended report is concerned, is this a good 
procedure?  That is to say, run my sequence through the Differential 
report possibly choosing a comp and check star (of those listed on the 
chart of course) that produce the flattest C2-C1 plot  then use the same 
two stars for the Extended report subsequently submitting the latter to 
the AAVSO database?

Best Regards,

John Ott