G_{i}(E_{j}) = D_{1}exp(-0.5 [(PI-D_{2})/D_{3}]^{2})

where PI indicates the i-th output channel.

As customary for proportional counters,
instead of the *sigma* one gives the FWHM as *Delta*E/E %.
The energy dependency is proportional to E^{-1/2}
and therefore a single parameter FWHM6 (the FWHM at 6 keV)
is sufficient to describe it:

- for M1 : ==> %
- for M2 : /poseidon/lucio/xas/calib/sax/mecs/resolution.coeff %
- for M3 : <== %

The *sigma* at any energy can therefore be easily computed as :

sigma = D_{3}= 0.01 FWHM6 6^{1/2}E^{1/2}/ 2.355