diff --git a/fit_waist.py b/fit_waist.py
index e708bbd..b099e2d 100755
--- a/fit_waist.py
+++ b/fit_waist.py
@@ -23,8 +23,8 @@ for f in files:
 	Pmes = data[:,1]
 
 	'''optimization with non-linear least squares method'''
-	Ppopt, Pcov = curve_fit(P, xmes, Pmes)
-	data_waist.append([int(f[-7:-4]), abs(Ppopt[3])])
+	Ppopt, Pcov = curve_fit(P, xmes, Pmes, method = 'trf')
+	data_waist.append([int(f[-7:-4]), Ppopt[3]])
 
 	'''plot'''
 	p[0].plot(xmes, Pmes, 'o')