The upper two graphs show the relationship between V1
and V2, which are the voltages required to achieve a 
sensitivity of 50A/lm and 500A/lm,  repectively.  (These 
numbers correspond to gains of 5x10**5 and 5x10**6 
respectively.)  At left are the SbCs PMs and at right are
the BeCu PMs.

The lower two graphs plot a quantity which is related to
gain.  Assume the PM gain/voltage relationship satisfies a
power law:

G = V**m

then dG/G = m dV/V and m is a measure of the sensitivity of
the PM gain to changes in voltage.  From the EMI gain 
measurements we can solve for m, using:

(V2/V1)**m = (G2/G1) 

then 

m = 2.3/(ln(V2)-ln(V1))

where ln(500/50) = 2.3.