diff --git a/cascade.py/dynamics/_simple_earth.py b/cascade.py/dynamics/_simple_earth.py
index 82281de..ca123eb 100644
--- a/cascade.py/dynamics/_simple_earth.py
+++ b/cascade.py/dynamics/_simple_earth.py
@@ -74,8 +74,9 @@ def simple_earth(
 
     .. note::
        If *drag* is active, the BSTAR coefficient (SI units) of the object must be passed as a first
-       simulation parameter in :class:`~cascade.sim`, if *SRP* is active, the object area (SI units) must be also passed as a
-       simulation parameter (after BSTAR if present).
+       simulation parameter in :class:`~cascade.sim`, if *SRP* is active, the term Cr*AOM (SI units) must be also passed as a
+       simulation parameter (after BSTAR if present), being Cr the coefficient of reflectivity of the spacecraft and AOM the 
+       area-to-mass-ratio.
 
 
     Args:
@@ -254,6 +255,7 @@ def simple_earth(
         Fm = phi_mp + phi_ma + phi_ms + (np.pi / 180) * 93.27283
         Dm = phi_mp + phi_ma - phi_m + (np.pi / 180) * 297.85027
 
+        # Careful, here we multiply by 1000 as the units are meters and not km as in the original paper where the eqs were presented.  
         rm = (
             385000
             - 20905 * hy.cos(lm)
diff --git a/doc/examples/20yearsofLEO_coll.ipynb b/doc/examples/20yearsofLEO_coll.ipynb
index c8e06a7..76952be 100644
--- a/doc/examples/20yearsofLEO_coll.ipynb
+++ b/doc/examples/20yearsofLEO_coll.ipynb
@@ -143,7 +143,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "dyn =  csc.dynamics.simple_earth(J2=True, J3=False, C22S22=True,sun=False,moon=False,SRP=False,drag=True)"
+    "dyn =  csc.dynamics.simple_earth(J2=True, J3=False, J4=False, C22S22=True,sun=False,moon=False,SRP=False,drag=True)"
    ]
   },
   {
diff --git a/doc/examples/oneweekofLEO_conj.ipynb b/doc/examples/oneweekofLEO_conj.ipynb
index 858d814..81a00b2 100644
--- a/doc/examples/oneweekofLEO_conj.ipynb
+++ b/doc/examples/oneweekofLEO_conj.ipynb
@@ -125,7 +125,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "dyn =  csc.dynamics.simple_earth(J2=True, J3 = False, C22S22=True, sun=False,moon=False,SRP=False,drag=True)"
+    "dyn =  csc.dynamics.simple_earth(J2=True, J3 = False, J4=False, C22S22=True, sun=False,moon=False,SRP=False,drag=True)"
    ]
   },
   {