K. Venkateswara, J. Kissel

Noticed BRS had been rung up with X-End activity (see LHO aLOG 13533).
- Gravity dance to damp the 8.8 [mHz] mode
- Changed very-low-frequency high-pass from 1 [mHz] to 0.5 [mHz], to improve signal fidelity for subtraction. 1 [mHz] was adding ~10 [deg] of phase to the signal at 10 [mHz] -- too much in the region we wish to use the BRS signal for GND T240.
- restarted code at ~11:45p PDT

Notes for future gravity dances:
- When Tilt signal is on the upper-half of its sign wave, one needs to stand on the North (+X) side, if lower-half on the south (-X) side.
- Transition, or start standing on a given side at the amplitude peak
- As the resonance gets damped, you need to stand on a given side for less and less time
- +/- 500 [ct] amplitude = need to stand on one side for a full half cycle (~30-50 seconds), +/-50 [ct] amplitude = only a few seconds at a time
- +/- 25 counts is good enough. 

Note on determining frequency for high-pass: 
- filter coefficient = (1 - (desired freq)/(sampling freq))
- Sampling frequency = 50 [Hz], desired frequency = 5e-4 [Hz] ==> filter coefficient = 0.99998;