reset

set xrange [0.9:2.1]
set yrange [10:55]

set title "Diagramm zur Aufgabe 1.4b"
set xlabel "[Spulenstrom {I} in A]"
set ylabel "[1/Kreisradius in 1/m]"
set grid xtics ytics

f(x) = m * x + a
g(x) = c * x + d

fit f(x) 'Datenem2.txt' us ($1):($2) via m,a
fit g(x) 'Datenem2.txt' us ($1):($3) via c,d

plot \
'Datenem2.txt' us ($1):($2) title "U = 125 V" lt 1, \
f(x) title "Ausgleichsgerade g3 (U = 125 V)" lt 1, \
'Datenem2.txt' us ($1):($3) title "U = 250 V" lt 3, \
g(x) title "Ausgleichsgerade g4 (U = 250 V)" lt 3

set output "em2.eps"
set term postscript enhanced eps color; replot