Fix to allow negative Values

src/PC/Helpers.elm

@@ -9,12 +9,21 @@ import Http         exposing (..)
 -- Please note that only 0 are added. The number will not be shortend!
 addLeadingZero : Int -> Int -> String
 addLeadingZero number length =
+    if number >= 0 then
         let
             num_str = String.fromInt number
         in
         (String.fromList <| List.repeat (length - String.length num_str) '0'
         )
         ++ num_str
+    else
+        let
+            num_str = String.fromInt <| 0-number
+        in
+        "-" ++
+        (String.fromList <| List.repeat (length - String.length num_str) '0'
+        )
+        ++ num_str
 
 
 -- Get the value at a given position in a List.