diff --git a/binarycpython/utils/useful_funcs.py b/binarycpython/utils/useful_funcs.py
index bda0da21239a098874acf74141b5bc3cbe5bf8d7..83f43d0a2bb9b35a7cbebaf06a6c9c57b958228d 100644
--- a/binarycpython/utils/useful_funcs.py
+++ b/binarycpython/utils/useful_funcs.py
@@ -22,7 +22,9 @@ YEARDY = 3.651995478818308811241877265275e02
 def calc_period_from_sep(M1, M2, sep):
     """
     calculate period from separation
-    args : M1, M2, separation (Rsun)
+    args : M1 (Msol), M2 (Msol), separation (Rsun)
+
+    returns the period (days)
     """
 
     return YEARDY * (sep / AURSUN) * math.sqrt(sep / (AURSUN * (M1 + M2)))
@@ -31,7 +33,9 @@ def calc_period_from_sep(M1, M2, sep):
 def calc_sep_from_period(M1, M2, period):
     """
     inverse of the above function
-    args : M1, M2, period (days)
+    args : M1 (Msol), M2 (Msol), period (days)
+
+    returns the separation (Rsun)
     """
 
     return AURSUN * (period * period * (M1 + M2) / (YEARDY * YEARDY)) ** (1.0 / 3.0)