diff --git a/sydney_tides.py b/sydney_tides.py
index 041febc..b4b2a5a 100644
--- a/sydney_tides.py
+++ b/sydney_tides.py
@@ -24,6 +24,10 @@ import math
 #
 # the harmonics included below in the python code were provided directly to WRL from BOM.
 
+START_TIME = '2020-01-01'
+END_TIME = '2020-12-31'
+OUTPUT_NAME = 'levels.csv'
+
 harm = {}
 speed = 0
 amp = 1
@@ -225,24 +229,24 @@ MSL = 0.9952
 
 # Now do the maths
 
-start_time = datetime.datetime(2019, 11, 29, 0, 0, 0)
-end_time = datetime.datetime(2019, 12, 5, 0, 0, 0)
+start_time = datetime.datetime.strptime(START_TIME, '%Y-%m-%d')
+end_time = datetime.datetime.strptime(END_TIME, '%Y-%m-%d')
 
 time_step = datetime.timedelta(minutes=15)
 
 x = []
 y = []
-F = open("tide.out", "w")
+F = open(OUTPUT_NAME, "w")
 t = start_time
 while (t < end_time):
     offset = t - datetime.datetime(t.year, 1, 1, 0, 0, 0)
-    yr = t.year - sy
+    year_idx = t.year - sy
     t1 = (offset.days) * 24.0 + offset.seconds / 3600.0
     z = MSL
     for constit in harm.keys():
         if constit in node_factor:
-            nf = node_factor[constit][yr]
-            ea = equalibrium_arg[constit][yr]
+            nf = node_factor[constit][year_idx]
+            ea = equalibrium_arg[constit][year_idx]
         else:
             nf = 1.0
             ea = 0.0