diff --git a/h-m-m b/h-m-m
index 29f6b3f..3145d3f 100755
--- a/h-m-m
+++ b/h-m-m
@@ -2728,6 +2728,38 @@ function mmput(&$mm,$x,$y,$s)
 }
 
 
+// }}}
+// {{{ rank
+
+function rank(&$mm, $add_positive, $add_negative)
+{
+
+	$negative = 0;
+	$positive = 0;
+	$existing = [];
+
+	if (mb_ereg('^\((\d+)\+,(\d+)\-\)', $mm['nodes'][ $mm['active_node'] ]['title'], $existing))
+	{
+		$positive = $existing[1];
+		$negative = $existing[2];
+		$mm['nodes'][ $mm['active_node'] ]['title'] =
+			mb_ereg_replace('^\(\d+\+,\d+\-\) *', '', $mm['nodes'][ $mm['active_node'] ]['title']);
+	}
+
+	$negative = max(0, $negative + $add_negative);
+	$positive = max(0, $positive + $add_positive);
+
+	$mm['nodes'][ $mm['active_node'] ]['title'] =
+		"({$positive}+,{$negative}-) "
+		.$mm['nodes'][ $mm['active_node'] ]['title']
+	;
+
+	$mm['modified'] = true;
+	build_map($mm);
+	display($mm);
+}
+
+
 // }}}
 // {{{ monitor key presses
 
@@ -2841,6 +2873,11 @@ function monitor_key_presses(&$mm)
 			case '?':       search($mm); break;
 			case ctrl_f:    search($mm); break;
 
+			case '=':       rank($mm, +1, 0); break;
+			case '+':       rank($mm, -1, 0); break;
+			case '-':       rank($mm,  0,+1); break;
+			case '_':       rank($mm,  0,-1); break;
+
 			case "\n":      insert_new_node($mm, insert_sibling); break;
 			case "\t":      insert_new_node($mm, insert_child); break;
 		}
diff --git a/readme.md b/readme.md
index c422680..a1251e5 100644
--- a/readme.md
+++ b/readme.md
@@ -22,11 +22,18 @@ Adding, removing, and editing nodes:
 * `Ctrl+p` - appends the clipboard text at the end of the active node's title
 * `e`, `i`, or `a` - edits the active node
 * `E`, `I`, or `A` - edits the active node, ignoring the existing text
-* `t` - toggles '✓ ', '✗ ', and '' at the beginning of the title
-* `#` - adds or removes sequential numbers at the beginning of the titles of a node and its siblings
 * `u` - undo
 * `Ctrl+r` - redo
 
+Marks:
+
+* `t` - toggles '✓ ', '✗ ', and '' at the beginning of the title
+* `#` - adds or removes sequential numbers at the beginning of the titles of a node and its siblings
+* `=` - increase the positive ranking
+* `+` - decrease the positive ranking
+* `-` - increase the negative ranking
+* `_` - decrease the negative ranking
+
 Relative navigating and moving:
 
 * `h` or `←` - activate the parent of the previously active node