determines the font parameters
param_g(ref_nbinter,thresh,font_axis)
ref_nbinter = # of chars that can be drawn on the x axis
thresh = # of chars in the title that causes a decline of 1 unit in the title font
font_axis= font of the axes
nothing: the parameters in saved in a scilab database
param_g(60,12,11,4) // Set the default values. param_g(40,9,8,3) // Set values suitable for smaller screens.