Displaying errors for uncomputable formulas in nutrients view

app/helpers/body_trackers_helper.rb

@@ -1,6 +1,13 @@
 module BodyTrackersHelper
   def format_value(value)
     amount, unitname = value
-    amount.nil? ? '-' : "#{amount} [#{unitname || '-'}]"
+    case
+    when amount.nil?
+      '-'
+    when amount.nan?
+      '?'
+    else
+      "#{amount} [#{unitname || '-'}]"
+    end
   end
 end