diff --git a/README.md b/README.md
index 708d5fa..d83f308 100644
--- a/README.md
+++ b/README.md
@@ -7,5 +7,5 @@ Python based radio frequency satellite tracking
 To view data attached as example:
 
 ```
-python .\rfplot.py  -p data -P 2021-08-04T20_48_35 -s 50 -l 1800 -C 4171
+python3 rfplot.py -p data -P 2021-08-04T20:48:35 -s 50 -l 1800 -C 4171
 ```
diff --git a/rfplot.py b/rfplot.py
index a0c51b2..d8128dc 100644
--- a/rfplot.py
+++ b/rfplot.py
@@ -16,14 +16,15 @@ from skyfield.api import load, wgs84, utc
 
 from modest import imshow
 
-if __name__ == "__main__":
+
+def main():
     mpl.rcParams['keymap.save'].remove('s')
     mpl.rcParams['keymap.fullscreen'].remove('f')
     mpl.rcParams['backend'] = "TkAgg"
 
     parser = argparse.ArgumentParser(description='rfplot: plot RF observations', formatter_class=argparse.ArgumentDefaultsHelpFormatter)
-    parser.add_argument('-p', help='Input path to parent directory /a/b/')
-    parser.add_argument('-P', help='Filename prefix c in c_??????.bin')
+    parser.add_argument('-p', help='Input path to parent directory /a/b/', required=True)
+    parser.add_argument('-P', help='Filename prefix c in c_??????.bin', required=True)
     parser.add_argument('-s', type=int, default=0,  help='Number of starting subintegration')
     parser.add_argument('-l', type=int, default=3600,  help='Number of subintegrations to plot')
     parser.add_argument('-C', type=int,  help='Site ID', default=4171)
@@ -214,3 +215,7 @@ if __name__ == "__main__":
     fig.canvas.mpl_connect('key_press_event', on_press)
     fig.canvas.mpl_connect('button_press_event', on_click)
     plt.show()
+
+
+if __name__ == "__main__":
+    main()