diff --git a/src/blocks/affineDecrypt.js b/src/blocks/affineDecrypt.js
index eec8bc3..1d6fb89 100644
--- a/src/blocks/affineDecrypt.js
+++ b/src/blocks/affineDecrypt.js
@@ -9,15 +9,15 @@ module.exports =  {
     },
     a: {
       name: "a",
-      type: "text",
+      type: "number",
       required: true,
-      inline: false
+      inline: true
     },
     b: {
       name: "b",
-      type: "text",
+      type: "number",
       required: true,
-      inline: false
+      inline: true
     }
   },
   output: true,
@@ -33,7 +33,7 @@ module.exports =  {
     }
 
     if(!require("./util/coPrime.js")(a, 26)){
-      console.log(a, 26, "not coprime");
+      throw "a and 26 must be coprime";
       return "";
     }
 
diff --git a/src/outputCalculation.js b/src/outputCalculation.js
index 011ea89..9fc1976 100644
--- a/src/outputCalculation.js
+++ b/src/outputCalculation.js
@@ -3,26 +3,35 @@ var events = require("./events.js");
 var blocks = require("./blocks");
 
 function resolveOutput(block, cache){
-  var inputValues = {};
-  for(var input in block.inputs){
-    if(block.inputs[input].joined){ //if it's joined to something else
-      if(block.inputs[input].joined in cache){ //if output of other block is already in cache
-        inputValues[input] = cache[block.inputs[input].joined];
+  try{
+    var inputValues = {};
+    var error = "";
+    for(var input in block.inputs){
+      if(block.inputs[input].joined){ //if it's joined to something else
+        if(block.inputs[input].joined in cache){ //if output of other block is already in cache
+          inputValues[input] = cache[block.inputs[input].joined];
+        }
+        else{
+          var inputBlock = diagram.state.filter((diagramBlock)=>(diagramBlock.id == block.inputs[input].joined))[0]; //find block instance
+          inputValues[input] = resolveOutput(inputBlock, cache); //calculate and store output
+        }
       }
-      else{
-        var inputBlock = diagram.state.filter((diagramBlock)=>(diagramBlock.id == block.inputs[input].joined))[0]; //find block instance
-        inputValues[input] = resolveOutput(inputBlock, cache); //calculate and store output
+      else if(block.inputs[input].value){ //if value is already set, just save that
+        inputValues[input] = block.inputs[input].value;
+      }
+      if(blocks[block.type].inputs[input].required && !(inputValues[input])){ //if input is required and is missing
+        throw "A required input is missing";
       }
     }
-    else if(block.inputs[input].value){ //if value is already set, just save that
-      inputValues[input] = block.inputs[input].value;
-    }
+
+    var output = blocks[block.type].execute(inputValues, block);
+    cache[block.id] = output;
+    return output;
+  }
+  catch(err){
+    console.log("ERROR", err);
+    return "";
   }
-
-  var output = blocks[block.type].execute(inputValues, block);
-  cache[block.id] = output;
-
-  return output;
 }
 
 function calculateOutputBlocks(){