diff --git a/aosstower/level_b1/nc.py b/aosstower/level_b1/nc.py
index 410c42206c4fc719804f04db42518d1f1d1e5501..e0621d75527d6ddfc8b12c47f5b5a36fba1f8765 100644
--- a/aosstower/level_b1/nc.py
+++ b/aosstower/level_b1/nc.py
@@ -467,7 +467,7 @@ def main():
     argparser.add_argument('-i', '--interval', type=float,
                            help='Width of the interval to average input data over in minutes.' +
                                 " If not specified, 1 is assumed. (Use 60 for one hour and 1440 for 1 day)")
-    argparser.add_argument('-cs', '--chunk-size', type=int, help='chunk Size for the netCDF file')
+    argparser.add_argument('--chunk-size', type=int, help='chunk size for the netCDF file')
     argparser.add_argument('-z', '--zlib', action='store_true', help='compress netCDF file with zlib')
 
     argparser.add_argument("input_files", nargs="+",