variables,gnuplot,curve-fitting,data-fitting,function-fitting

Quoting the documentation: If activated by using set fit errorvariables, the error for each fitted parameter will be stored in a variable named like the parameter, but with "_err" appended. ...

python,data-fitting,function-fitting

Here are a couple of observations that could help: You could try the least-squares fit directly with leastsq, providing the Jacobian, which might help tame it. I'm guessing you don't want the superconducting temperatures in your data set at all if you're fitting to an Einstein model (do you have...

csv,plot,gnuplot,function-fitting

You can use the solution offered in the comments with a system() call, or use stats: Option 1: N = floor(system("wc -l output.csv")/100.) Option 2: stats output.csv N = floor(STATS_records/100.) ...