diff --git a/collective_effects/instabilities.py b/collective_effects/instabilities.py
index 99842e9f6bcc319c56cf7e411c6e58b582cf0544..9ac662286995fbe5a40d0a3e629d4802f85c0ef8 100644
--- a/collective_effects/instabilities.py
+++ b/collective_effects/instabilities.py
@@ -50,6 +50,9 @@ def cbi_threshold(ring, I, Vrf, f, beta, Ncav=1):
     """
     Compute the longitudinal and transverse coupled bunch instability 
     thresolds driven by HOMs [1].
+    
+    Approximate formula, does not take into account variation with Q.
+    For better estimate use lcbi_growth_rate.
 
     Parameters
     ----------
diff --git a/collective_effects/tapers.py b/collective_effects/tapers.py
index 8d944e2b84c772ceb99823fc57783c41daabf209..7703621998216230bdea5d7a7519813dc1df6086 100644
--- a/collective_effects/tapers.py
+++ b/collective_effects/tapers.py
@@ -5,7 +5,7 @@ Created on Tue Mar 31 13:15:36 2020
 @author: gamelina
 """
 
-from scipy.constants import mu_0, epsilon_0, c, pi
+from scipy.constants import mu_0, c, pi
 import numpy as np
 from scipy.integrate import trapz
 from mbtrack2.collective_effects.wakefield import WakeField, Impedance
diff --git a/collective_effects/utilities.py b/collective_effects/utilities.py
index 5a57ca97c595bf88e4fb9d5386e9d86490dc1b09..a2d3858e2d889bcf80700ee3d31f7455bf267ead 100644
--- a/collective_effects/utilities.py
+++ b/collective_effects/utilities.py
@@ -13,7 +13,6 @@ from pathlib import Path
 from scipy.interpolate import interp1d
 from scipy.constants import c
 from mbtrack2.collective_effects.wakefield import Impedance, WakeFunction, WakeField
-from pathlib import Path
 
 
 def read_CST(file, impedance_type='long', divide_by=None):
diff --git a/collective_effects/wakefield.py b/collective_effects/wakefield.py
index 36b37f2e8d1060aa13ad6a8b9ec1363128cd202f..6097bbd15eadb7a411fe27a8121ed6f3aee370b0 100644
--- a/collective_effects/wakefield.py
+++ b/collective_effects/wakefield.py
@@ -8,7 +8,6 @@ wake functions.
 """
 
 import warnings
-import re
 import pandas as pd
 import numpy as np
 import scipy as sc
diff --git a/tracking/synchrotron.py b/tracking/synchrotron.py
index aba2b58872f01752fc47b703c3471c6628e5d59b..92515510a3a4bebfafc39c9a7aeef1ff2714704d 100644
--- a/tracking/synchrotron.py
+++ b/tracking/synchrotron.py
@@ -87,6 +87,7 @@ class Synchrotron:
     -------
     synchrotron_tune(Vrf)
         Compute synchrotron tune from RF voltage.
+    sigma(position)
     """
     def __init__(self, h, optics, particle, **kwargs):
         self._h = h
@@ -239,19 +240,19 @@ class Synchrotron:
     
     def sigma(self, position=None):
         """
-        RMS beam size at equilibrium
+        Return the RMS beam size at equilibrium in [m].
 
         Parameters
         ----------
         position : float or array, optional
-            Longitudinal position where the beam size is computed. If None, 
-            the local values are used.
+            Longitudinal position in [m] where the beam size is computed. 
+            If None, the local values are used.
 
         Returns
         -------
         sigma : array
-            RMS beam size at position location or at local positon if position
-            is None.
+            RMS beam size in [m] at position location or at local positon if 
+            position is None.
 
         """
         if position is None:
diff --git a/tracking/wakepotential.py b/tracking/wakepotential.py
index 9741ef5b2a368248be7db54cd9e27b8ea9664150..061d4ebc4a08137f91bd949f7fa886c29f009312 100644
--- a/tracking/wakepotential.py
+++ b/tracking/wakepotential.py
@@ -12,7 +12,7 @@ import matplotlib.pyplot as plt
 import pandas as pd
 from scipy import signal
 from scipy.interpolate import interp1d
-from scipy.constants import mu_0, epsilon_0, c, pi
+from scipy.constants import mu_0, c, pi
 from mbtrack2.tracking.element import Element
 from mbtrack2.collective_effects.utilities import gaussian_bunch