The mass of the object being monitored keeps shrinking.  The old seismometers had big masses on a spring, or supported by a wire and able to swing.  But as electronic techniques make the measurement of position faster, smaller and more precise, the big masses are stil useful.

That is why I am trying to instrument a simple pendulum with precise sensors.

But follow the thought all the way down.

The "atom interferometers" make use of the fact that the wavelength for a particle is h/mv, where h is Planck's constant , m is the mass of the particle, and v is the velocity of the particle. The larger the mass of the particle being used, the smaller the wavelength.  

h = 6.626070040E-34 Joules/Hertz

But other than some experiments with atom interferometer chips, the cost and complexity of the "atom" methods seems difficult to implement.  I will keep looking, but will it is hard to find something I can adapt during this short period of this contest.  Oh, most of the "quantum" experiments with Bose Einstein condensates, including some superconducting configurations can be treated as simple atom methods.

My note here goes to still smaller particles, the electrons.  These are used in large quantities in our current (pun intended) devices.  We store them in our capacitors, move them from place to place, modulate them, and find them generally fairly useful

But we have not (so far as I have found yet) used the fact they have mass that is sensitive to gravitational potential (time dilation effects), and gravitational potential gradients (acceleration and velocity effects).  The atom interferometers make use of well studied internal states of atoms and molecules to manipulate and monitor them for use in sensing.  But there are very very specific interactions of electrons that can as well.

I do not like the term "spin spin", because it doesn't tell me what is happening or what I can do with it.  I like the term "permanent magnetic dipole interaction".  I will put up with "hyperfine interaction" when it is applied to interactions of magnetic dipoles, magnetic quadupoles or any combination of Schrodinger states of atoms, molecules or particles.  If it can be represented as a "particle" whose field has multipoles, and these interact, I would say "multipole interactions".

So I am looking at all the electron magnetic dipole interactions to see which phenomena might be "hacked" to make a low cost, small, precise gravimeter.

One magnetic dipole interaction I have used for a long time is electron-electron magnetic dipole binding, where two electrons bind magnetically to form a stable pair.  I think that is the basis of supeconductivity generally, but I am trying to stay on track to solve this gravimeter problem in time. I am pretty sure the same thing is going on with proton-proton magnetic dipole binding in neutron stars and everyday nuclei here on earth.  I use magnetic dipole binding to estimate nuclear reactions where particles with permanent magnetic dipoles bind with nuclear energies. Sorry, just reminding myself of all the pathways I have investigated over the years.  I want one to help me here.

So in a radio receiver, the fluctuations in the voltage of the electrons in a capacitor are related to "kT".  But part of that signal is gravity, part is the earth's magnetic field, part seismic, part human noise, and part kinetic fluctuations and phonons in the parts.  We distinguish "kT" in resistors, but it is just the same mix of signals coming through the potentials affecting particular devices in our circuits called resistors.  I tried to use a "kT" sensor (Johnson noise) sensor recently, but so far inconclusive, because you have to measure "everything" to sort out the source of the noise. 

So, in parallel, I am gathering data from magnetometer arrays, seismometer arrays, gravimeter arrays, VLF ELF ULF and all frequencies of electromagnetic sources, power system noise --- any signal that is coming in from anywhere to affect the pendulum, and the electronics.

So, perhaps, my "pendulum" is any oscillator.  Maybe electrons in a capacitor, or the specific collection of electrons in a resistor.  Or electrons in a coil.  It has to be big and unique enough to track with current (pun intended) technology, but low cost and easy to adapt.

I am not forgetting photons in ring lasers either.  The Sagnac effect is very useful.  It is just so expensive still.  I will check if anyone has hacked the fiber ring laser interferometer for gravimetry.  Maybe I need to check rotation as well.  :)

Sorry for all the speciallized terms.  But that is how people keep track of the phenomena and capabilities of these kinds of devices and processes.

So sorting out all the possibilities and how things work, is helpful.  I just hope I can focus to get this particular device working soon.