minor update

7 years ago · 0e29a4d18a
parent 1e842e4789
commit 0e29a4d18a
1 changed files with 5 additions and 1 deletions
--- a/pyModeS/adsb.py
+++ b/pyModeS/adsb.py
@ -679,4 +679,8 @@ def altitude_diff(msg):
    msgbin = util.hex2bin(msg)
    sign = -1 if int(msgbin[80]) else 1
    value = util.bin2int(msgbin[81:88]) * 25
-    return sign * value
+
+    if value == 0 or value == 127:
+        return None
+    else:
+        return sign * value