diff --git a/generate/elong_test.js b/generate/elong_test.js
index ffc48adf..2edf447c 100644
--- a/generate/elong_test.js
+++ b/generate/elong_test.js
@@ -2,6 +2,86 @@
 const fs = require('fs');
 const Astronomy = require('../source/js/astronomy.js');
 
+function SearchElongTest() {
+    // Max elongation data obtained from:
+    // http://www.skycaramba.com/greatest_elongations.shtml
+    TestMaxElong('Mercury', '2010-01-17T05:22Z', '2010-01-27T05:22Z', 24.80, 'morning');
+    TestMaxElong('Mercury', '2010-05-16T02:15Z', '2010-05-26T02:15Z', 25.10, 'morning');
+    TestMaxElong('Mercury', '2010-09-09T17:24Z', '2010-09-19T17:24Z', 17.90, 'morning');
+    TestMaxElong('Mercury', '2010-12-30T14:33Z', '2011-01-09T14:33Z', 23.30, 'morning');
+    TestMaxElong('Mercury', '2011-04-27T19:03Z', '2011-05-07T19:03Z', 26.60, 'morning');
+    TestMaxElong('Mercury', '2011-08-24T05:52Z', '2011-09-03T05:52Z', 18.10, 'morning');
+    TestMaxElong('Mercury', '2011-12-13T02:56Z', '2011-12-23T02:56Z', 21.80, 'morning');
+    TestMaxElong('Mercury', '2012-04-08T17:22Z', '2012-04-18T17:22Z', 27.50, 'morning');
+    TestMaxElong('Mercury', '2012-08-06T12:04Z', '2012-08-16T12:04Z', 18.70, 'morning');
+    TestMaxElong('Mercury', '2012-11-24T22:55Z', '2012-12-04T22:55Z', 20.60, 'morning');
+    TestMaxElong('Mercury', '2013-03-21T22:02Z', '2013-03-31T22:02Z', 27.80, 'morning');
+    TestMaxElong('Mercury', '2013-07-20T08:51Z', '2013-07-30T08:51Z', 19.60, 'morning');
+    TestMaxElong('Mercury', '2013-11-08T02:28Z', '2013-11-18T02:28Z', 19.50, 'morning');
+    TestMaxElong('Mercury', '2014-03-04T06:38Z', '2014-03-14T06:38Z', 27.60, 'morning');
+    TestMaxElong('Mercury', '2014-07-02T18:22Z', '2014-07-12T18:22Z', 20.90, 'morning');
+    TestMaxElong('Mercury', '2014-10-22T12:36Z', '2014-11-01T12:36Z', 18.70, 'morning');
+    TestMaxElong('Mercury', '2015-02-14T16:20Z', '2015-02-24T16:20Z', 26.70, 'morning');
+    TestMaxElong('Mercury', '2015-06-14T17:10Z', '2015-06-24T17:10Z', 22.50, 'morning');
+    TestMaxElong('Mercury', '2015-10-06T03:20Z', '2015-10-16T03:20Z', 18.10, 'morning');
+    TestMaxElong('Mercury', '2016-01-28T01:22Z', '2016-02-07T01:22Z', 25.60, 'morning');
+    TestMaxElong('Mercury', '2016-05-26T08:45Z', '2016-06-05T08:45Z', 24.20, 'morning');
+    TestMaxElong('Mercury', '2016-09-18T19:27Z', '2016-09-28T19:27Z', 17.90, 'morning');
+    TestMaxElong('Mercury', '2017-01-09T09:42Z', '2017-01-19T09:42Z', 24.10, 'morning');
+    TestMaxElong('Mercury', '2017-05-07T23:19Z', '2017-05-17T23:19Z', 25.80, 'morning');
+    TestMaxElong('Mercury', '2017-09-02T10:14Z', '2017-09-12T10:14Z', 17.90, 'morning');
+    TestMaxElong('Mercury', '2017-12-22T19:48Z', '2018-01-01T19:48Z', 22.70, 'morning');
+    TestMaxElong('Mercury', '2018-04-19T18:17Z', '2018-04-29T18:17Z', 27.00, 'morning');
+    TestMaxElong('Mercury', '2018-08-16T20:35Z', '2018-08-26T20:35Z', 18.30, 'morning');
+    TestMaxElong('Mercury', '2018-12-05T11:34Z', '2018-12-15T11:34Z', 21.30, 'morning');
+    TestMaxElong('Mercury', '2019-04-01T19:40Z', '2019-04-11T19:40Z', 27.70, 'morning');
+    TestMaxElong('Mercury', '2019-07-30T23:08Z', '2019-08-09T23:08Z', 19.00, 'morning');
+    TestMaxElong('Mercury', '2019-11-18T10:31Z', '2019-11-28T10:31Z', 20.10, 'morning');
+    TestMaxElong('Mercury', '2010-03-29T23:32Z', '2010-04-08T23:32Z', 19.40, 'evening');
+    TestMaxElong('Mercury', '2010-07-28T01:03Z', '2010-08-07T01:03Z', 27.40, 'evening');
+    TestMaxElong('Mercury', '2010-11-21T15:42Z', '2010-12-01T15:42Z', 21.50, 'evening');
+    TestMaxElong('Mercury', '2011-03-13T01:07Z', '2011-03-23T01:07Z', 18.60, 'evening');
+    TestMaxElong('Mercury', '2011-07-10T04:56Z', '2011-07-20T04:56Z', 26.80, 'evening');
+    TestMaxElong('Mercury', '2011-11-04T08:40Z', '2011-11-14T08:40Z', 22.70, 'evening');
+    TestMaxElong('Mercury', '2012-02-24T09:39Z', '2012-03-05T09:39Z', 18.20, 'evening');
+    TestMaxElong('Mercury', '2012-06-21T02:00Z', '2012-07-01T02:00Z', 25.70, 'evening');
+    TestMaxElong('Mercury', '2012-10-16T21:59Z', '2012-10-26T21:59Z', 24.10, 'evening');
+    TestMaxElong('Mercury', '2013-02-06T21:24Z', '2013-02-16T21:24Z', 18.10, 'evening');
+    TestMaxElong('Mercury', '2013-06-02T16:45Z', '2013-06-12T16:45Z', 24.30, 'evening');
+    TestMaxElong('Mercury', '2013-09-29T09:59Z', '2013-10-09T09:59Z', 25.30, 'evening');
+    TestMaxElong('Mercury', '2014-01-21T10:00Z', '2014-01-31T10:00Z', 18.40, 'evening');
+    TestMaxElong('Mercury', '2014-05-15T07:06Z', '2014-05-25T07:06Z', 22.70, 'evening');
+    TestMaxElong('Mercury', '2014-09-11T22:20Z', '2014-09-21T22:20Z', 26.40, 'evening');
+    TestMaxElong('Mercury', '2015-01-04T20:26Z', '2015-01-14T20:26Z', 18.90, 'evening');
+    TestMaxElong('Mercury', '2015-04-27T04:46Z', '2015-05-07T04:46Z', 21.20, 'evening');
+    TestMaxElong('Mercury', '2015-08-25T10:20Z', '2015-09-04T10:20Z', 27.10, 'evening');
+    TestMaxElong('Mercury', '2015-12-19T03:11Z', '2015-12-29T03:11Z', 19.70, 'evening');
+    TestMaxElong('Mercury', '2016-04-08T14:00Z', '2016-04-18T14:00Z', 19.90, 'evening');
+    TestMaxElong('Mercury', '2016-08-06T21:24Z', '2016-08-16T21:24Z', 27.40, 'evening');
+    TestMaxElong('Mercury', '2016-12-01T04:36Z', '2016-12-11T04:36Z', 20.80, 'evening');
+    TestMaxElong('Mercury', '2017-03-22T10:24Z', '2017-04-01T10:24Z', 19.00, 'evening');
+    TestMaxElong('Mercury', '2017-07-20T04:34Z', '2017-07-30T04:34Z', 27.20, 'evening');
+    TestMaxElong('Mercury', '2017-11-14T00:32Z', '2017-11-24T00:32Z', 22.00, 'evening');
+    TestMaxElong('Mercury', '2018-03-05T15:07Z', '2018-03-15T15:07Z', 18.40, 'evening');
+    TestMaxElong('Mercury', '2018-07-02T05:24Z', '2018-07-12T05:24Z', 26.40, 'evening');
+    TestMaxElong('Mercury', '2018-10-27T15:25Z', '2018-11-06T15:25Z', 23.30, 'evening');
+    TestMaxElong('Mercury', '2019-02-17T01:23Z', '2019-02-27T01:23Z', 18.10, 'evening');
+    TestMaxElong('Mercury', '2019-06-13T23:14Z', '2019-06-23T23:14Z', 25.20, 'evening');
+    TestMaxElong('Mercury', '2019-10-10T04:00Z', '2019-10-20T04:00Z', 24.60, 'evening');
+    TestMaxElong('Venus', '2010-12-29T15:57Z', '2011-01-08T15:57Z', 47.00, 'morning');
+    TestMaxElong('Venus', '2012-08-05T08:59Z', '2012-08-15T08:59Z', 45.80, 'morning');
+    TestMaxElong('Venus', '2014-03-12T19:25Z', '2014-03-22T19:25Z', 46.60, 'morning');
+    TestMaxElong('Venus', '2015-10-16T06:57Z', '2015-10-26T06:57Z', 46.40, 'morning');
+    TestMaxElong('Venus', '2017-05-24T13:09Z', '2017-06-03T13:09Z', 45.90, 'morning');
+    TestMaxElong('Venus', '2018-12-27T04:24Z', '2019-01-06T04:24Z', 47.00, 'morning');
+    TestMaxElong('Venus', '2010-08-10T03:19Z', '2010-08-20T03:19Z', 46.00, 'evening');
+    TestMaxElong('Venus', '2012-03-17T08:03Z', '2012-03-27T08:03Z', 46.00, 'evening');
+    TestMaxElong('Venus', '2013-10-22T08:00Z', '2013-11-01T08:00Z', 47.10, 'evening');
+    TestMaxElong('Venus', '2015-05-27T18:46Z', '2015-06-06T18:46Z', 45.40, 'evening');
+    TestMaxElong('Venus', '2017-01-02T13:19Z', '2017-01-12T13:19Z', 47.10, 'evening');
+    TestMaxElong('Venus', '2018-08-07T17:02Z', '2018-08-17T17:02Z', 45.90, 'evening');
+}
+
 function LoadData(filename) {
     const text = fs.readFileSync(filename, {encoding:'utf8'});
     const lines = text.trimRight().split('\n');
@@ -77,9 +157,9 @@ function TestMaxElong(body, startText, verifyText, verifyAngle, verifyVisibility
     let verifyDate = new Date(verifyText);
     let evt = Astronomy.SearchMaxElongation(body, startDate);
 
-    let hour_diff = Math.abs(verifyDate - evt.time.date) / (1000 * 3600);
+    let hour_diff = (verifyDate - evt.time.date) / (1000 * 3600);
     let angle_diff = Math.abs(evt.elongation - verifyAngle);
-    console.log(`TestMaxElong: ${body.padStart(8)} ${evt.visibility.padStart(8)} elong=${evt.elongation.toFixed(2).padStart(5)} (err ${angle_diff.toFixed(2).padStart(4)})  ${evt.time.toString()} (err ${hour_diff.toFixed(2).padStart(4)} hours)`);
+    console.log(`TestMaxElong: ${body.padStart(8)} ${evt.visibility.padStart(8)} elong=${evt.elongation.toFixed(2).padStart(5)} (err ${angle_diff.toFixed(2).padStart(4)})  ${evt.time.toString()} (err ${hour_diff.toFixed(2).padStart(5)} hours)`);
 
     if (evt.visibility !== verifyVisibility)
         throw `TestMaxElong: expected visibility ${verifyVisibility}, but found ${evt.visibility}`;
@@ -87,7 +167,7 @@ function TestMaxElong(body, startText, verifyText, verifyAngle, verifyVisibility
     if (angle_diff > 1.0)
         throw `TestMaxElong: excessive angular error = ${angle_diff}`;
 
-    if (hour_diff > 5)
+    if (Math.abs(hour_diff) > 15)
         throw `TestMaxElong: excessive hour error = ${hour_diff}`;
 }
 
@@ -100,11 +180,7 @@ for (let body of ['Mercury', 'Venus'])
 for (let body of ['Mars', 'Jupiter', 'Saturn', 'Uranus', 'Neptune', 'Pluto'])
     TestPlanet(`temp/longitude_${body}.txt`, body, 1700, 2200, 'opp');
 
-// Correct answers for max elongation from:
-// https://www.thenauticalalmanac.com/Astronomical_Phenomena_for_the_year_2019.pdf
-TestMaxElong('Mercury', '2019-01-01T00:00Z', '2019-02-27T01:00Z', 18.0, 'evening');
-TestMaxElong('Mercury', '2019-03-01T00:00Z', '2019-04-11T20:00Z', 28.0, 'morning');
-TestMaxElong('Venus',   '2018-12-01T00:00Z', '2019-01-06T05:00Z', 47.0, 'morning');
+SearchElongTest();
 
 console.log('elong_test.js: SUCCESS')
 process.exit(0);
diff --git a/generate/template/astronomy.js b/generate/template/astronomy.js
index 427c2528..260c4ae8 100644
--- a/generate/template/astronomy.js
+++ b/generate/template/astronomy.js
@@ -1954,7 +1954,7 @@ Astronomy.SearchMaxElongation = function(body, startDate) {
     let startTime = AstroTime(startDate);
 
     const table = {
-        Mercury : { s1:55.0, s2:75.0 },
+        Mercury : { s1:50.0, s2:85.0 },
         Venus :   { s1:40.0, s2:50.0 }
     };
 
@@ -2015,6 +2015,7 @@ Astronomy.SearchMaxElongation = function(body, startDate) {
         let m1 = neg_slope(t1);
         if (m1 >= 0) 
             throw `SearchMaxElongation: internal error: m1 = ${m1}`;
+
         let m2 = neg_slope(t2);
         if (m2 <= 0) 
             throw `SearchMaxElongation: internal error: m2 = ${m2}`;
diff --git a/source/js/astronomy.js b/source/js/astronomy.js
index 64be8e79..6bb2d3cc 100644
--- a/source/js/astronomy.js
+++ b/source/js/astronomy.js
@@ -2791,7 +2791,7 @@ Astronomy.SearchMaxElongation = function(body, startDate) {
     let startTime = AstroTime(startDate);
 
     const table = {
-        Mercury : { s1:55.0, s2:75.0 },
+        Mercury : { s1:50.0, s2:85.0 },
         Venus :   { s1:40.0, s2:50.0 }
     };
 
@@ -2852,6 +2852,7 @@ Astronomy.SearchMaxElongation = function(body, startDate) {
         let m1 = neg_slope(t1);
         if (m1 >= 0) 
             throw `SearchMaxElongation: internal error: m1 = ${m1}`;
+
         let m2 = neg_slope(t2);
         if (m2 <= 0) 
             throw `SearchMaxElongation: internal error: m2 = ${m2}`;