 Find a resonance frequency (minimal break off distance), then vary the sheath pressure to optimize the jet using this calculator.
 The current jet velocity v is distance / time where distance is the span from the bottom of the last
attached drop (breakoff) to the same point on a drop n drops below,
and time is the number of drops in the span x the drop period (1/ddf). The optimal frequency f_{opt} is calculated:
f_{opt} = v / 4.5d_{j}
where the estimated contracted jet diameter d_{j} is 0.975 x the nozzle diameter d_{d}. See reference for more.
