minor attempt at improvement

fitter.py

@@ -69,8 +69,8 @@ class Fitter:
         )
 
         states = self.initial_values
-        t = self.tspan
-        V = model.mem_potential(t)
+
+        V = self.model.mem_potential(t)
         _calc_curr = model.calculated_current(states, t, V)
         calculated_current = (
             self.convolve_current(_calc_curr, tau=tau_RC)[self.current_time_indecies]