diff --git a/src/CacheSim/Raw.elm b/src/CacheSim/Raw.elm
index 6dfc6eb..8084f7f 100644
--- a/src/CacheSim/Raw.elm
+++ b/src/CacheSim/Raw.elm
@@ -21,11 +21,11 @@ translateRawCacheModel rcm =
             (Just bs, Just sc, Just ss) ->
                 Ok { blockSize = bs, setCount = sc, setSize = ss }
             (Nothing, _, _) ->
-                Err <| "Unable to parse the block size: " ++ rcm.blockSize
+                Err <| "Unable to parse the block size: \"" ++ rcm.blockSize ++ "\""
             (_, Nothing, _) ->
-                Err <| "Unable to parse the set count: " ++ rcm.setCount
+                Err <| "Unable to parse the set count: \"" ++ rcm.setCount ++ "\""
             (_, _, Nothing) ->
-                Err <| "Unable to parse the set size: " ++ rcm.setSize
+                Err <| "Unable to parse the set size: \"" ++ rcm.setSize ++ "\""
 
 translateRawCacheModelHierarchy : RawCacheModelHierarchy -> Result String CacheModelHierarchy
 translateRawCacheModelHierarchy rcmh =
@@ -42,8 +42,8 @@ validateCacheModelHierarchy cmh =
         [] -> Ok []
         x::[] -> Ok [x]
         x::y::xs ->
-            if modBy y.blockSize x.blockSize == 0
+            if modBy x.blockSize y.blockSize == 0
             then validateCacheModelHierarchy (y::xs)
-            else Err <| "Block cache size " ++ String.fromInt x.blockSize ++
+            else Err <| "Block cache size " ++ String.fromInt y.blockSize ++
                 " is not a multiple of the next level cache's" ++
-                " block size (" ++ String.fromInt y.blockSize ++ ")"
+                " block size (" ++ String.fromInt x.blockSize ++ ")"
diff --git a/src/CacheSim/View.elm b/src/CacheSim/View.elm
index 11b3a7f..f574b3a 100644
--- a/src/CacheSim/View.elm
+++ b/src/CacheSim/View.elm
@@ -2,9 +2,16 @@ module CacheSim.View exposing (..)
 import CacheSim.Raw exposing (..)
 import CacheSim.Model exposing (..)
 import Html exposing (Html, input, text, div, label, span, h2, h3)
-import Html.Attributes exposing (type_, class, value, for)
+import Html.Attributes exposing (type_, class, value, for, classList, disabled)
 import Html.Events exposing (onInput, onClick)
 
+optionalButton : Bool -> String -> Msg -> Html Msg
+optionalButton e s m =
+    let
+        events = if e then [ onClick m ] else  [ disabled (not e) ]
+    in
+        input ([ type_ "button", value s ] ++ events) []
+
 button : String -> Msg -> Html Msg
 button s m = input [ type_ "button", onClick m, value s] []
 
@@ -45,11 +52,30 @@ viewRawCacheModelHierarchy rcmh =
     let
         models = div [ class "cache-model-levels" ] 
             <|List.indexedMap viewRawCacheModel rcmh
+        translationResult = Result.andThen validateCacheModelHierarchy
+            <| translateRawCacheModelHierarchy rcmh
+        isValid =
+            case translationResult of
+                Ok _ -> True
+                Err _ -> False
+        errorHtml =
+            case translationResult of
+                Ok _ -> viewError True ""
+                Err e -> viewError False e
         
         newButton = button "Add level" CreateRawModel
+        useButton = optionalButton isValid "Use hierarchy" CreateRawModel
     in
         div [ class "cache-model-hierarchy" ]
             [ h2 [] [ text "Cache hierarchy" ]
-            , buttonWrapper [ newButton ]
+            , errorHtml
+            , buttonWrapper [ newButton, useButton ]
             , models
             ]
+
+viewError : Bool -> String -> Html Msg
+viewError hide e = span [ classList [ ("hidden", hide) ] ] [ text e ]
+
+viewBase : Model -> Html Msg
+viewBase m =
+    div [] [ viewRawCacheModelHierarchy m.rawHierarchy ]
diff --git a/src/Main.elm b/src/Main.elm
index 9e8b1cf..3a5ce63 100644
--- a/src/Main.elm
+++ b/src/Main.elm
@@ -24,7 +24,7 @@ init f =
 view : Model -> Document Msg
 view m =
     { title = "Cache Simulator"
-    , body = [ viewRawCacheModelHierarchy m.rawHierarchy ]
+    , body = [ viewBase m ]
     }
 
 update : Msg -> Model -> (Model, Cmd Msg)