gistfile1.diff

   def can_compute_performance?(start_date, end_date)
-    !checking? && (balances.count(:select => 'distinct period', :conditions => { :period => (start_date..end_date)}) > 1)
+    has_at_least_one_period = balances.count(
+      :select => 'distinct period',
+      :conditions => {:period => (start_date..end_date)}
+    ) > 1
+    is_not_checking = !checking?
+
+    is_not_checking && has_at_least_one_period
   end