fit a+b*x 'm101a.txt' using (($1-50)**0.25):((log($2-350)) )  via a,b

plot 'm101a.txt' using (($1-50)**0.25):((log($2-350)) ) with point , "m101a.txt" using (($1-50)**0.25):(a+b* (($1-50)**0.25))  with line 3