I've posted my question about the effect on the amplitude from adding mass to a pendulum bob. I didn't receive a useful reply, so I made an app. that conversely drops a mass from the bob of a pendulum at ~ any desired time. I haven't though of a method that adds mass w/o "disturbing" the P. other than just adding mass.
Pics of the app. are here:
Index of /Horological/weight pan effect/Magnetic drop
I've collected data for one trial; dropping the mass very soon after passing BDC on its upward swing. The RMS gives position data from which one may also plot the angular speed of the P.
Care to predict the result? Which I'll post after fitting: Angle = A (exp(-C0*t))(sin(2Pi *f * t + C1)) + C2, I pray.