cat measure dat gnuplot gnuplot gnuplot fit measure dat via Final set

$ cat measure.dat 
0 0
1 2
2 4
3 6
$ gnuplot
gnuplot> f(x) = a*x + b
gnuplot> fit f(x) 'measure.dat' via a, b
...
Final set of parameters 
======================= 

a               = 2              
b               = 2.60475e-35