J. Kissel, E. Goetz

Since we haven't had a number to reflect the answer to perennial question  "what's the status of the calibration?" in what *feels* like a long time (the last time we were able to quantify its badness was on on 2019-01-31, based on a measurement from 2019-01-18, see LHO:46723), I've been given time to take a PCAL to DELTAL_EXTERNAL sweep today.

As a result of successfully gathering this sweep, I was able to -- offline -- correct all* systematic errors in the DELTAL_EXTERNAL ASD, and compute the range -- at one time -- 120 seconds of data starting at 2019-02-19 23:00 UTC. This time was a thermally stabilized, and otherwise undisturbed with all calibration lines on. The plot aide is attached, but the sweep indicated a frequency dependent systematic error with excursions as high as 20%. 
The conclusion is that DELTAL_EXTERNAL is under-reporting H1's range by (85.45 - 75.35)/85.45 = 0.1182 ~ 12%.
*This is, of course, assuming PCAL is a perfect calibrator. It should be damn close as the PCAL Y recently had a tune-up and remeasure of its force coefficient -- see LHO:46695, but I only balk a bit because of the recent evidence for clipping -- see LHO:46847.

While I can't specifically attribute the systematic error to any one thing, I can point you to an aLOG in which I describe the current (well -- 2 weeks ago now) status of what I believe I need to do in order to correctly *remove* this systematic error: LHO:46806. Sadly, because of the snow-blizzard and lack of person power, I haven't made much *tangible* progress at all.

The data lives here:
    (1) 2019-02-19_H1_PCAL2DARM_TF_5t1100Hz_8min.xml [Contains both DELTAL / PCAL and C/(1+G) measurements]
    (2) 2019-02-19_H1DARM_OLGTF_5to1100Hz_20min.xml [Contains both G and 1/(1+G) measurements]
    (3) 2019-02-19_H1_OMCDCPDSUM_to_DARMIN1.xml [Contains information to turn DARM IN1 counts roughly into DCPD SUM Current in "mA"]
Note -- I only *need* needed measurement (1), but I was generously given a bit more time.

I've worked my way through using Evan's command line function,
    /ligo/svncommon/CalSVN/aligocalibration/trunk/Common/pyDARM/correct_bns_range.py

It required I create a new loop model,
    /ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/O3/H1/params
        modelparams_H1_20190219.py

The exact command line sequence I used for the function is 
python3.6 correct_bns_range.py --run='O3' --IFO='H1' --GPSstart='1234652418' --GPSend='1234652538' --PCAL2DARMTF='/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/O3/H1/Measurements/FullIFOSensingTFs/2019-02-19_H1_PCAL2DARMTF_A_PCALYRX_B_DELTALEXT_tf.txt' --PCAL2DARMCOH='/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/O3/H1/Measurements/FullIFOSensingTFs/2019-02-19_H1_PCAL2DARMTF_A_PCALYRX_B_DELTALEXT_coh.txt' --DARMmodelfile='modelparams_H1_20190219' --modelFunction='modelPars'