diff --git a/README.md b/README.md
index 5f10e2a..6339203 100644
--- a/README.md
+++ b/README.md
@@ -1,3 +1,6 @@
 # lstrend
 
-Show trend data for files changing size
\ No newline at end of file
+Show trend data for files changing size
+
+usage: lstrend [-h] files [files ...]
+
diff --git a/lstrend b/lstrend
new file mode 100755
index 0000000..6b20deb
--- /dev/null
+++ b/lstrend
@@ -0,0 +1,55 @@
+#!/usr/bin/python3
+
+import argparse
+import os
+import time
+
+factor = 0.99
+
+def get_sizes(files):
+    sizes = []
+    for file in files:
+        sizes.append(os.path.getsize(file))
+    return sizes
+
+def human_format(num):
+    num = float('{:.3g}'.format(num))
+    magnitude = 0
+    while abs(num) >= 1024:
+        magnitude += 1
+        num /= 1024.0
+    return '{}{}'.format('{:.3f}'.format(num).rstrip('0').rstrip('.'), ['', 'K', 'M', 'G', 'T', 'P'][magnitude])
+
+def lstrend(files):
+    avgrates = None
+    sizes = None
+    stamp = None
+    while True:
+        lastsizes = sizes
+        laststamp = stamp
+        sizes = get_sizes(files)
+        stamp = time.monotonic()
+        if lastsizes:
+            diffs  = [s-lastsizes[c] for c,s in enumerate(sizes)]
+            tdelta = stamp-laststamp
+            rates  = [s/tdelta for s in diffs]
+            if avgrates:
+                avgrates = [avgrates[c]*factor+r*(1-factor) for c,r in enumerate(rates)]
+            else:
+                avgrates = rates
+            print()
+            for c,file in enumerate(files):
+                print("{: <20} {: >10} {: >10}".format(file, human_format(avgrates[c]), human_format(sizes[c])))
+        time.sleep(1)
+
+
+def main():
+    parser = argparse.ArgumentParser(description='Show trend in file size')
+    parser.add_argument('files', nargs='+', help='files to list')
+
+    args = parser.parse_args()
+
+    lstrend(args.files)
+
+if __name__ == "__main__":
+    main()