set term X11 enhanced

f1(x) = a1*tanh(x/b1)            # define the function to be fit
a1 = 300; b1 = 0.005;            # initial guess for a1 and b1
fit f1(x) 'force.dat' using 1:2 via a1, b1

f2(x) = a2 * tanh(x/b2)            # define the function to be fit
a2 = 300; b2 = 0.005;            # initial guess for a and b
fit f2(x) 'force.dat' using 1:3 via a2, b2

set key at 0.018,150 title "F(x) = A tanh (x/B)"             # title to key!
set title "Force Deflection Data \n and curve fit"      # note newline!
set pointsize 1.5                              # larger point!
set xlabel 'Deflection, {/Symbol D}_x (m)'            # Greek symbols!
set ylabel 'Force, {/Times-Italic F}_A, (kN)'            # italics!

plot    "force.dat" using 1:2 title 'Column data' with points pt 3, \
      "force.dat" using 1:3 title 'Beam data'   with points pt 4, \
      a1 * tanh( x / b1 ) title 'Column-fit: A=309, B=0.00227', \
      a2 * tanh( x / b2 ) title 'Beam-fit: A=260, B=0.00415'

#set output 'force.ps'                                      #creates ps output
#set term post land color
#replot

#unset output                                               #close file
#set term qt enhanced
reset                                                      #back to default values