diff --git a/lib/cartodb/server_options.js b/lib/cartodb/server_options.js
index 4938c709..6cf28c66 100644
--- a/lib/cartodb/server_options.js
+++ b/lib/cartodb/server_options.js
@@ -11,7 +11,7 @@ var   _          = require('underscore')
 module.exports = function(){
 
     var rendererConfig = _.defaults(global.environment.renderer || {}, {
-      cache_ttl: 60000,
+      cache_ttl: 60000, // milliseconds
       metatile: 4,
       bufferSize: 64
     });