diff --git a/GasFill_GUI.py b/GasFill_GUI.py
index 4c7c68a7ba17866f1a31bf4b46eb1a52fd47ccbd..8eefb08923358f663eb83644d1ece6dd4dcf15b0 100644
--- a/GasFill_GUI.py
+++ b/GasFill_GUI.py
@@ -18,19 +18,17 @@ import sys
 import GasFill_times
 
 
-
 #fiber variables
 dia_tube = 0.02 #(mm) capillary diameter
 len_tube = 2.7 #(m)
 #gas variables
 P = 10 #(mbar) average pressure inside capillary
-mW = 26.04 #(g/mol)
+mW = 28.97 #(g/mol)
 temp = 21 #(degC) Temperature of system
-dia_mol = 3.34 #(pm) diameter of gas molecule
+dia_mol = 359.99 #(pm) diameter of gas molecule
 # execute only if run as the entry point into the program
 
 
-
 class GafFillGUI(QWidget):
     
     def __init__(self):
diff --git a/GasFill_times.py b/GasFill_times.py
index 68335a8699f4527f9ff724fc345b9b4dd37d6ddc..be857ee285cbf2aab7bdd42fa86835eb7ff6da61 100644
--- a/GasFill_times.py
+++ b/GasFill_times.py
@@ -24,7 +24,7 @@ def filltime (dia_tube,len_tube,P,mW,temp,dia_mol):
 	dia_tube = dia_tube / 1000 #(m)
 	rad_tube = rad_tube / 1000 #(m)
 	temp = temp + 273.15 #(K)
-	dia_mol = 3.34 / 10000000000 #(m)
+	dia_mol = 359.99 / 1000000000000 #(m)
 	mW = 26.04 / 1000 #(kg/mol)
 	mM = mW / 6.02214e23 #(kg)
 
@@ -66,7 +66,7 @@ if __name__ == '__main__':
     P = 10 #(mbar) average pressure inside capillary
     mW = 26.04 #(g/mol)
     temp = 21 #(degC) Temperature of system
-    dia_mol = 3.34 #(pm) diameter of gas molecule
+    dia_mol = 359.99 #(pm) diameter of gas molecule
     # execute only if run as the entry point into the program
     
     filltime(dia_tube,len_tube,P,mW,temp,dia_mol)
diff --git a/README.md b/README.md
index 50d2ac1ac33279cb9df60ca3bbb1ef39e3bd3ab9..621be7cbca37107d9f9a61366926ec8a5afeede5 100644
--- a/README.md
+++ b/README.md
@@ -16,7 +16,14 @@ scipy
 
 ### Instructions
 
-Run: GasFill_GUI.py
+Run: GasFill_GUI.py  
+Entre the values you wish to test and click calculate to get an accurate fill time.  
+Core Diameter: This is the diameter of the fibre that will be filled with air.  
+Fibre length: Length of the fibre to be filled with gas.  
+Temperature: Temperature of the fiber and gas under test.  
+Molecular weight: In mixed gasses this is the average molecular weight of the gas in air this is ~28.97 g/mol.  
+Molecular diameter: In mixed gasses this is the average kinetic diameter of the gas molcucules. In air this is 359.99 pm.  
+
 
 ## Authors