diff --git a/src/blocks/caesar.js b/src/blocks/caesar.js
index 4dfec60..0ccecbb 100644
--- a/src/blocks/caesar.js
+++ b/src/blocks/caesar.js
@@ -11,7 +11,8 @@ module.exports =  {
       name: "Shift",
       type: "number",
       required: true,
-      inline: true
+      inline: true,
+      default: "0"
     }
   },
   output: true,
diff --git a/src/blocks/hexToAscii.js b/src/blocks/hexToAscii.js
index 21bea8b..66dc26e 100644
--- a/src/blocks/hexToAscii.js
+++ b/src/blocks/hexToAscii.js
@@ -25,7 +25,7 @@ module.exports =  {
     .filter((pair)=>(pair.length == 2))
     .map((pair)=>(parseInt(pair, 16)))
     .map((int)=>(String.fromCharCode(int)))
-    .join("")
+    .join("");
   },
   pageBlock: {
     html: "",
diff --git a/src/blocks/lettersToNums.js b/src/blocks/lettersToNums.js
index b0bc52b..4d9fb1b 100644
--- a/src/blocks/lettersToNums.js
+++ b/src/blocks/lettersToNums.js
@@ -10,19 +10,13 @@ module.exports =  {
     offset: {
       name: "Offset",
       type: "text",
-      required: true,
-      inline: false
+      required: false,
+      inline: false,
+      default: "0"
     }
   },
   output: true,
   execute: function({letters, offset}, elem){
-    if(!offset){
-      offset = 0;
-    }
-    else{
-      offset = parseInt(offset);
-    }
-
     return letters
     .split("")
     .map((char)=>(char.charCodeAt(0)))
@@ -35,7 +29,7 @@ module.exports =  {
         return asciiVal - 97;
       }
     })
-    .map((num)=>(num + offset))
+    .map((num)=>(num + parseInt(offset)))
     .map((num)=>(((num%26)+26)%26))
     .join(",");
   },
diff --git a/src/blocks/numsToLetters.js b/src/blocks/numsToLetters.js
index 0677018..6e41319 100644
--- a/src/blocks/numsToLetters.js
+++ b/src/blocks/numsToLetters.js
@@ -10,34 +10,20 @@ module.exports =  {
     offset: {
       name: "Offset",
       type: "text",
-      required: true,
-      inline: false
+      required: false,
+      inline: false,
+      default: "0"
     }
   },
   output: true,
   execute: function({nums, offset}, elem){
-    if(!offset){
-      offset = 0;
-    }
-    else{
-      offset = parseInt(offset);
-    }
-
     return nums
     .split(",")
     .filter((num)=>(num))
     .map((num)=>(parseInt(num)))
     .filter((num)=>(!isNaN(num)))
-    .map((num)=>(num - offset))
-    .map((num)=>(num%52))
-    .map((num)=>{
-      if(num < 0){
-        return 52 + num;
-      }
-      else{
-        return num;
-      }
-    })
+    .map((num)=>(num - parseInt(offset)))
+    .map((num)=>((num%52)+52)%52)
     .map((num)=>{
       if(num < 26){
         asciiOffset = 97;
diff --git a/src/outputCalculation.js b/src/outputCalculation.js
index 9fc1976..ab0f76a 100644
--- a/src/outputCalculation.js
+++ b/src/outputCalculation.js
@@ -5,7 +5,7 @@ var blocks = require("./blocks");
 function resolveOutput(block, cache){
   try{
     var inputValues = {};
-    var error = "";
+    $(block.elem).find(".error").html("");
     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
@@ -19,8 +19,13 @@ function resolveOutput(block, cache){
       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";
+      if(!inputValues[input]){ //if currently missing/blank
+        if(blocks[block.type].inputs[input].default){ //if a default is present, use that
+          inputValues[input] = blocks[block.type].inputs[input].default;
+        }
+        else if(blocks[block.type].inputs[input].required){ //otherwise, throw an error
+          throw "A required input is missing";
+        }
       }
     }
 
@@ -28,8 +33,8 @@ function resolveOutput(block, cache){
     cache[block.id] = output;
     return output;
   }
-  catch(err){
-    console.log("ERROR", err);
+  catch(err){ //if there is an error, display it
+    $(block.elem).find(".error").html(err);
     return "";
   }
 }
diff --git a/src/pageInteraction/block.hbs b/src/pageInteraction/block.hbs
index 5b20b82..12ffbe2 100644
--- a/src/pageInteraction/block.hbs
+++ b/src/pageInteraction/block.hbs
@@ -12,6 +12,7 @@
   <div class="main">
     <div>
       <div class="title">{{block.name}}</div>
+      <div class="error"></div>
       {{{block.pageBlock.html}}}
     </div>
   </div>
diff --git a/src/styles.scss b/src/styles.scss
index 4616eaa..ef228b2 100644
--- a/src/styles.scss
+++ b/src/styles.scss
@@ -61,6 +61,10 @@ body{
       >.title{
         text-align: center;
       }
+      >.error{
+        color: red;
+        text-align: center;
+      }
     }
   }
   >.output{