[doc] some more error rate explanation and other minor tweaks

NEWS

@@ -17,7 +17,7 @@ lnav v0.8.1:
        same data discover/extraction parser used in the 'logline' table.
      * Added a "summary" overlay line to the bottom of the log view that
        displays how long ago the last message was received, along with the
-       total number of files, errors, and warnings.
+       total number of files and the error rate over the past five minutes.
      * Pressing 'V' in the DB view will now check for a column with a
        timestamp and move to the corresponding time in the log view.
      * Added 'a/A' hotkeys to restore a view previously popped with 'q/Q'.

src/help.txt

@@ -121,6 +121,17 @@ left and right hand side of the bar, for search hits and bookmarks.
 When multiple files are open, a bar on the left side is color coded and
 broken up to indicate which messages are from the same file.
 
+When at the bottom of the log view, a summary line will be displayed on the
+right-hand-side to give you some more information about your logs, including:
+how long ago the last message was generated, the number of log files, the
+error rate, and how much time the logs cover.  The error rate display shows
+the errors-per-minute over the last five minutes.  A bar chart is also
+overlaid on the "Error rate" label to show the error rate over the past ten
+seconds.  For example, if there have not been many errors in the past five
+minutes and there is a sudden spike, the bar chart will fill up completely.
+But, if there has been a steady stream of errors, then the chart will only
+partially fill based on the recent error frequency.
+
 Above and below the main body are status lines that display:
 
   * the current time;

src/relative_time.cc

@@ -333,11 +333,15 @@ size_t str2reltime(int64_t millis, std::string &value_out)
         {    0, NULL, NULL }
     };
 
-    struct rel_interval *curr_interval;
+    struct rel_interval *curr_interval = intervals;
     size_t in_len = value_out.length(), retval = 0;
 
-    for (curr_interval = intervals; curr_interval->symbol != NULL;
-         curr_interval++) {
+    if (millis >= (10 * 60 * 1000)) {
+        millis /= 1000;
+        curr_interval += 1;
+    }
+
+    for (; curr_interval->symbol != NULL; curr_interval++) {
         long long amount;
         char      segment[32];
 
@@ -347,7 +351,7 @@ size_t str2reltime(int64_t millis, std::string &value_out)
         }
         else {
             amount = millis;
-            millis   = 0;
+            millis = 0;
         }
 
         if (!amount && !millis) {