We have fitted the RA and Dec deviations as a function of roll angle
obtaining the following best fits:

(1a)

(1b)

(2a)

(2b)

where is the value of the roll angle expressed in degrees.

These best fits have been plotted as solid lines in Figures 2 and 3 respectively.

A separate fit of MECS1, MECS2 and MECS3 data has been performed. Since very small differences (of the order of 2-3 arcsec) between the three units have been found, we have adopted a single correction formula for MECS data, obtained averaging the best fit parameters of the three units.

Equations (1) and (2) can been used to correct LECS and MECS event files
coordinates. The correction is obtained *adding*
and
to the LECS and MECS coordinates:

A specific task (**saxposcor**) that corrects LECS and MECS event
files has been developed and is available at /bepposax/saxposcor/saxposcor.html