diff --git a/app/models/estimate.rb b/app/models/estimate.rb
index 6de04b3..c93212a 100644
--- a/app/models/estimate.rb
+++ b/app/models/estimate.rb
@@ -14,6 +14,11 @@ class Estimate < ActiveRecord::Base
   belongs_to :customer 
   validates_presence_of :doc_number, :id
   self.primary_key = :id
+
+  # returns a human readable string
+  def to_s
+    return self[:doc_number]
+  end
   
   # sync all estimates
   def self.sync
diff --git a/app/models/invoice.rb b/app/models/invoice.rb
index 264895c..47b1460 100644
--- a/app/models/invoice.rb
+++ b/app/models/invoice.rb
@@ -14,6 +14,11 @@ class Invoice < ActiveRecord::Base
   belongs_to :customer 
   validates_presence_of :doc_number, :id, :customer_id, :txn_date
   self.primary_key = :id
+
+   # returns a human readable string
+  def to_s
+    return self[:doc_number]
+  end
   
   # sync ALL the invoices
   def self.sync