diff --git a/lib/pebble.js b/lib/pebble.js
index 37118e383ee..67f4236bc48 100644
--- a/lib/pebble.js
+++ b/lib/pebble.js
@@ -30,12 +30,14 @@ function pebble (req, res) {
         console.log('queried', new Date(earliest_data).toISOString( ),
                     new Date(now).toISOString( ), 'got raw results', results.length);
         results.forEach(function(element, index, array) {
-            var last = cgmData[cgmData.length - 1];
+            var next = null;
+            if (index + 1 < results.length) {
+              next = results[index + 1];
+            }
             if (element) {
-                console.log(element, index);
                 var obj = {};
                 obj.sgv = element.sgv;
-                obj.bgdelta = (last ? (last.sgv - element.sgv) : 0);
+                obj.bgdelta = (next ? (element.sgv - next.sgv ) : 0);
                 if ('direction' in element) {
                   obj.trend = directionToTrend(element.direction);
                   obj.direction = element.direction;